What would it take for renewably powered electrosynthesis to displace petrochemical processes?
可再生能源电合成需要什么才能取代石化过程？

Electrochemical activation and conversion of CO₂ and water into hydrocarbons and oxygenates could potentially offer a sustainable route to produce many of the world’s most needed commodity chemicals (Fig. 1A). Coupling renewable sources of energy (solar, wind, hydroelectric) with electrochemical reduction of CO₂ to chemicals, if done efficiently, could address the nondispatchable nature of renewables by providing storage in chemical bonds. Electrocatalysis also provides a route to transforming carbon resources into chemicals without the need to burn carbon fuels, assuming the CO₂ is taken from air. At present, direct air CO₂ capture is far from industrially mature, but recent work has shown a pathway toward a cost of $94 to $232 per tonne of CO₂ from the atmosphere (8), with startup companies such as Carbon Engineering and Climeworks having secured funding to scale CO₂ capture processes to industrially relevant levels. However, electrocatalysis is currently limited to C1 to C3 chemical production for two major reasons: (i) Higher carbon species require more proton-coupled electron transfers, leading to a highly complex reaction pathway and poor product selectivities (9), and (ii) there is a diminishing energy return per number of electrons transferred as the carbon number increases (10).
电化学活化 ₂ 和将一氧化碳和水转化为碳氢化合物和含氧化合物可能为生产许多世界上最需要的商品化学品提供一条可持续的途径（图1A）。将可再生能源（太阳能、风能、水力发电）与一氧化碳 ₂ 电化学还原为化学品相结合，如果有效地完成，可以通过提供化学键的储存来解决可再生能源的不可调度性。电催化还提供了一种将碳资源转化为化学品的途径，而无需燃烧碳燃料，假设一氧化碳 ₂ 是从空气中提取的。目前，直接空气中一氧化碳 ₂ 捕获远未成熟，但最近的研究表明， ₂ 从大气中每吨一氧化碳的成本为94美元至232美元（8），Carbon Engineering和Climeworks等初创公司已获得资金，将一氧化碳 ₂ 捕获过程扩展到工业相关水平。然而，电催化目前仅限于 C1 到 C3 的化学生产，主要有两个原因：（i） 更高的碳种类需要更多的质子耦合电子转移，导致高度复杂的反应途径和较差的产物选择性 （9），以及 （ii） 随着碳数的增加，每转移一个电子数的能量回报就会递减 （10）。

There exist commercial electrochemical technologies that offer a blueprint for CO₂ electroconversion. Of these options, water electrolyzers that produce hydrogen and oxygen are the most analogous and industrially mature, with companies such as Siemens, Proton OnSite, Teledyne, Nel Hydrogen, and Hydrogenics selling commercial-scale electrolyzers. The global water electrolysis market is expected to grow from $8.5 billion (USD) today to $11 billion by 2023, driven mostly by the chemical industry’s desire for emissions-free sources of hydrogen (11). Although electrochemical hydrogen production today accounts for 4% of total hydrogen production (with the remainder from steam reforming of natural gas and coal gasification), this represents 8 GW of electrolysis capacity (12, 13). The total market is $115 billion and is expected to reach $155 billion by 2022, with up to 8% of the growth coming from electrolysis (12). Natural gas as a feedstock is currently cheap because of the shale gas revolution in North America. However, in the long term, electrolysis may be a more sustainable process. The energy landscape is evolving quickly, with renewables gaining market share. If technological challenges are overcome, electrochemical processes based on renewable electricity may become more cost-effective. In addition to water electrolysis, the research community has also been focusing on photoelectrochemical water splitting as a means of decentralized energy conversion and storage (14, 15). The topic of hydrogen evolution has been covered in many excellent reviews (5, 16–19) and will not be further explored here.
现有的商业电化学技术为一氧化碳 ₂ 电转化提供了蓝图。在这些选项中，产生氢气和氧气的水电解槽是最相似的，也是工业上最成熟的，西门子、Proton OnSite、Teledyne、Nel Hydrogen 和 Hydrogenics 等公司都在销售商业规模的电解槽。全球水电解市场预计将从目前的 85 亿美元增长到 2023 年的 110 亿美元，这主要是由于化工行业对无排放氢气来源的渴望 （11）。尽管今天电化学制氢占总制氢量的4%（其余来自天然气的蒸汽重整和煤气化），但这代表了8 GW的电解能力（12,13）。总市场规模为 1150 亿美元，预计到 2022 年将达到 1550 亿美元，其中高达 8% 的增长来自电解 （12）。由于北美的页岩气革命，天然气作为原料目前很便宜。然而，从长远来看，电解可能是一个更可持续的过程。能源格局正在迅速发展，可再生能源的市场份额越来越大。如果克服了技术挑战，基于可再生电力的电化学工艺可能会变得更具成本效益。除了水电解之外，研究界还一直关注光电化学水分解作为分散能量转换和储存的手段（14,15）。氢析出的主题已经在许多优秀的评论中涉及（5,16-19），这里不再进一步探讨。

Electrochemical carbon dioxide reduction (CO₂R) has seen a marked increase in research activity over the past few years. It offers a prospectively sustainable pathway for producing fuel and chemical feedstocks through the electrochemical conversion of an undesirable greenhouse gas. The Faradaic efficiencies (Fig. 1B) and energy conversion efficiencies (Table 1) toward many CO₂R products have increased steadily over the past 30 years. Current densities have also increased to >100 mA/cm² (Fig. 1B) as a result of the adoption of gas diffusion electrodes that overcome the CO₂ solubility limit in aqueous electrolytes. Production of simpler C1 products such as CO and formic acid has become possible with high initial selectivity even on simple metal foils. However, more sophisticated catalyst, electrolyte, and cell engineering is required to make substantial improvements in selectivity for C2 products because of the difficulty of C-C coupling. Additionally, efficient product separation and recycling of unreacted CO₂ is another practical concern that could be mitigated by improvements in catalyst selectivity. The topic of materials design for CO₂R electrocatalysis has also been covered extensively by multiple reviews (20–27). Here, we instead focus on the barriers that this technology would have to surmount to disrupt the chemical industry.
在过去几年中，电化学二氧化碳还原（CO ₂ R）的研究活动显着增加。它为通过电化学转化不良温室气体来生产燃料和化学原料提供了一种具有前景的可持续途径。在过去30年中，许多CO ₂ R产品的法拉第效率（图1B）和能量转换效率（表1）稳步提高。电流密度也增加到>100 mA/cm ² （图1B），这是由于采用了气体扩散电极，克服了水电解质中CO ₂ 的溶解度极限。即使在简单的金属箔上，也可以很容易地生产更简单的 C1 产品，例如 CO 和甲酸，并且具有很高的初始选择性。然而，由于 C-C 偶联的困难，需要更复杂的催化剂、电解质和电池工程来大幅提高 C2 产物的选择性。此外，未反应的一氧化碳的高效产物分离和回收 ₂ 是另一个实际问题，可以通过提高催化剂选择性来缓解。CO ₂ R 电催化的材料设计主题也被多篇综述广泛涵盖 （20–27）。在这里，我们关注的是这项技术必须克服的障碍，以颠覆化学工业。

Decades of research have proven effective in developing efficient catalysts for the electrochemical generation of hydrogen and oxygen from water to the point of commercialization. Because these electrochemical transformations require, in principle, similar components to CO₂R, lessons learned from the engineering scale-up and device design of hydrogen electrolyzers can be of great utility.
数十年的研究证明，在开发高效催化剂方面是有效的，该催化剂用于从水中电化学生成氢气和氧气，直至商业化。由于这些电化学转化原则上需要与 CO ₂ R 相似的组件，因此从氢电解槽的工程放大和设备设计中吸取的经验教训可能非常有用。

Several factors uniquely position the electrochemical conversion of CO₂ for accelerated technological development. First, the products of CO₂R already exist within many petrochemical supply chains, and therefore the chemical industry infrastructure is more readily prepared to adapt to CO₂R. Second, the need to reduce emissions along with the gradual adoption of carbon capture technologies is resulting in large energy consumers and carbon emitters facing the challenge of what to do with the CO₂ once it is captured (10). CO₂R provides a way to recover value from what would otherwise be a tremendous sunk cost. The Carbon XPRIZE is a $20 million competition to capture and convert the most CO₂ and is jointly funded by COSIA, a consortium of large oil producers (28).
有几个因素使CO的电化学转化 ₂ 具有独特的优势，可以加速技术发展。首先，一氧化碳 ₂ 产品已经存在于许多石化供应链中，因此化工行业的基础设施更容易适应一氧化碳 ₂ 。其次，随着碳捕获技术的逐步采用，减少排放的需要导致大型能源消费者和碳排放者面临着 ₂ 一氧化碳被捕获后如何处理的挑战（10）。CO ₂ R 提供了一种从原本巨大的沉没成本中回收价值的方法。Carbon XPRIZE是一项耗资2000万美元的竞赛，旨在捕获和转化最多的一氧化碳 ₂ ，由大型石油生产商财团COSIA共同资助（28）。

Governments worldwide have identified climate change initiatives as having high priority. For example, China, the world’s largest energy consumer and carbon emitter, recently announced $360 billion in renewable energy investments by 2020 in an effort to reduce carbon emissions (29). Canada is implementing a carbon pricing policy federally with a current tax of $10/tonne CO₂ and a steady rise to $50/tonne CO₂ nationwide by 2022. Mission Innovation, a 22-country global initiative to accelerate clean energy innovation, has named CO₂ Capture and Utilization, Clean Energy Materials, and Converting Sunlight as topics of innovation challenges.
世界各国政府已将气候变化倡议确定为高度优先事项。例如，中国是世界上最大的能源消费国和碳排放国，最近宣布到2020年将投资3600亿美元的可再生能源，以减少碳排放（29）。加拿大正在联邦实施碳定价政策，目前的碳税为10美元/吨一氧化碳 ₂ ，到2022年 ₂ 全国范围内将稳步上升到50美元/吨一氧化碳。Mission Innovation 是一项由 22 个国家/地区组成的全球倡议，旨在加速清洁能源创新，将 CO ₂ 捕获和利用、清洁能源材料和转换阳光列为创新挑战的主题。

Despite a favorable ecosystem for renewable chemical feedstocks, industrial scale-up still entails challenges and risks. For example, electrolytes must be optimized with careful consideration of cost, environmental impact, and availability to reach the scales necessary for meaningful emissions reductions. Public policy concerning CO₂ utilization technologies needs to be carefully crafted and social acceptance of the field needs to be managed. Carbon taxes, nationwide caps on CO₂ emissions, and certifications of CO₂-derived products are examples of public policy tools. From a societal acceptance point of view, people need to be educated about how carbon capture and sequestration is different from carbon capture and utilization. Most important, catalysts and system efficiencies for this technology need to be vastly improved to be economically viable with minimal or no government subsidies (because it is difficult to rationalize sustainable business models based on subsidies and policies that can be easily changed).
尽管可再生化学原料拥有有利的生态系统，但工业规模化仍面临挑战和风险。例如，电解质必须经过优化，仔细考虑成本、环境影响和可用性，以达到有意义的减排所需的规模。需要仔细制定有关一氧化碳 ₂ 利用技术的公共政策，并需要管理该领域的社会接受度。碳税、全国范围内的一氧化碳 ₂ 排放上限以及一氧化碳 ₂ 衍生产品的认证都是公共政策工具的例子。从社会接受的角度来看，人们需要接受教育，了解碳捕获和封存与碳捕获和利用有何不同。最重要的是，这项技术的催化剂和系统效率需要大幅提高，才能在经济上可行，而政府补贴很少或没有政府补贴（因为很难根据补贴和政策来合理化可持续的商业模式，而这些补贴和政策很容易改变）。

Many technoeconomic analyses of solar fuels have analyzed the needed Faradaic efficiencies and energy efficiencies required to match fossil fuel–derived sources (10, 30–34). Among them, the largest influence on the levelized cost of production (the net present value of the cost of electricity over the lifetime of the asset) has consistently been the price of electricity. Building on previous studies, we have calculated the cost of electrosynthesized hydrogen, carbon monoxide, ethanol, and ethylene as a function of the energy conversion efficiency and electricity cost (Fig. 2) to provide a comparison to current market prices. We also provide a sensitivity analysis on production cost as a function of carbon emissions–free electricity source, showing nuclear and geothermal as currently the most cost-competitive (fig. S2; see supplementary text for calculation details). We note that commodity chemical prices are highly variable with respect to geographic region and feedstock (see below). Using optimistic assumptions based on industrially mature polymer electrolyte membrane (PEM) water electrolyzer specifications, we show that when electricity costs fall below 4 cents/kWh and energy efficiency is at least 60%, all products become competitive with current market prices for these products derived from fossil fuel sources. These calculations assume amortization over a plant lifetime of 30 years, a common period for industrial power plants (35). Replacing initial capital-intensive infrastructure would carry additional costs. To put this into perspective, the best systems today have demonstrated full cell energy efficiencies of approximately 40 to 50% for CO, approaching cost-competitive targets. Considering that CO₂R to CO technologies are in the early stages of development, it is expected that with further catalyst and electrochemical cell designs, improved performance can be obtained. From an electricity cost perspective, renewable prices continue to plummet. Between 2010 and 2017, average global utility-scale solar plants fell 73% to 10 cents/kWh and onshore wind fell by 23% to 6 cents/kWh, with some projects consistently delivering electricity for 4 cents/kWh (36). Recent onshore wind power auctions in Brazil, Canada, Germany, India, Mexico, and Morocco have shown levelized electricity costs as low as 3 cents/kWh, within the range of profitability of electrosynthesized chemicals (36). Costs have fallen as a result of increased economies of scale, greater competition, and advances in the manufacturing of crystalline silicon. This cost decrease in renewable technologies provides an optimistic and aggressive goal for electrocatalytic technologies.
许多对太阳能燃料的技术经济分析已经分析了匹配化石燃料衍生来源所需的法拉第效率和能源效率（10,30-34）。其中，对平准化生产成本（资产生命周期内电力成本的净现值）影响最大的一直是电价。在以往研究的基础上，我们计算了电合成氢气、一氧化碳、乙醇和乙烯的成本与能源转换效率和电力成本的关系（图2），以提供与当前市场价格的比较。我们还对生产成本作为无碳排放电力来源的函数进行了敏感性分析，显示核能和地热是目前最具成本竞争力的（图S2;计算细节见补充文本）。我们注意到，大宗化学品价格因地理区域和原料而异（见下文）。使用基于工业成熟的聚合物电解质膜 （PEM） 水电解槽规格的乐观假设，我们表明，当电力成本低于 4 美分/千瓦时且能源效率至少为 60% 时，所有产品都与这些来自化石燃料的产品的当前市场价格具有竞争力。这些计算假设工厂寿命为30年，这是工业电厂的常见时期（35）。更换初始资本密集型基础设施将带来额外的成本。从这个角度来看，当今最好的系统已经证明，一氧化碳的全电池能量效率约为 40% 至 50%，接近具有成本竞争力的目标。 考虑到CO ₂ R-CO技术处于早期发展阶段，预计通过进一步的催化剂和电化学电池设计，可以获得更高的性能。从电力成本的角度来看，可再生能源价格继续暴跌。2010年至2017年间，全球公用事业规模的太阳能发电厂平均发电量下降了73%，至10美分/千瓦时，陆上风电下降了23%，至6美分/千瓦时，一些项目一直以4美分/千瓦时的速度提供电力（36）。最近在巴西、加拿大、德国、印度、墨西哥和摩洛哥进行的陆上风电拍卖显示，平准化电力成本低至3美分/千瓦时，在电合成化学品的盈利范围内（36）。由于规模经济的增加、竞争的加剧以及晶体硅制造的进步，成本已经下降。可再生技术成本的降低为电催化技术提供了一个乐观而积极的目标。

To quantify the potential impact of electrochemical synthesis of common carbon-based commodity chemicals on carbon emissions, we performed a life-cycle assessment for formic acid, carbon monoxide, ethylene, and ethanol. Of these products, ethylene has the largest global market size at $230 billion and the highest current production emissions of 862 Mt CO₂e per year (Fig. 3A); these numbers suggest that renewably synthesized ethylene is an attractive target for meaningful global warming impact reduction (37). The electricity grid carbon intensity (the amount of carbon dioxide emitted per kWh of electricity generated) and the energy conversion efficiency were found to be the most sensitive factors affecting overall CO₂ emissions (Fig. 3, B to E). We note that capital expenditure factors such as construction and electrode materials were not considered. Assuming a plant capacity of 500 MW, an average grid intensity for the European Union (0.295 kg CO₂e/kWh in 2016) (38), and an energy conversion efficiency of 70%, carbon monoxide and formic acid result in carbon emissions that are lower than fossil fuel–derived sources. In order for products to reduce carbon emissions compared to current production, the grid carbon intensity needs to be 0.11 kg CO₂e/kWh or lower. It should be noted that an energy conversion efficiency of 70% has not yet been demonstrated for all products considered herein.
为了量化常见碳基商品化学品的电化学合成对碳排放的潜在影响，我们对甲酸、一氧化碳、乙烯和乙醇进行了生命周期评估。在这些产品中，乙烯的全球市场规模最大，为2300亿美元，目前产量最高，为每年862公吨二氧化碳 ₂ 当量（图3A）;这些数字表明，可再生合成乙烯是有意义的减少全球变暖影响的一个有吸引力的目标（37）。电网碳强度（每千瓦时发电量排放的二氧化碳量）和能源转换效率是影响总CO ₂ 排放量的最敏感因素（图3，B至E）。我们注意到，没有考虑建筑和电极材料等资本支出因素。假设电厂容量为500兆瓦，欧盟的平均电网强度（2016年为0.295千克二氧化碳 ₂ 当量/千瓦时）（38），能源转换效率为70%，一氧化碳和甲酸导致的碳排放量低于化石燃料衍生来源。与当前生产相比，为了使产品减少碳排放，电网碳强度需要为 0.11 kg CO ₂ e/kWh 或更低。应该注意的是，对于本文所考虑的所有产品，尚未证明70%的能量转换效率。

To benchmark these results, we provide a comparison of electrocatalytic, biocatalytic, and traditional fossil fuel–derived processes for ethylene, carbon monoxide, ethanol, and formic acid production (Table 2). Bio-ethylene production using bio-ethanol precursors is economically competitive in Brazil because of the ample availability of cheap sugarcane feedstock (39). Petrochemical ethylene is produced mainly from steam cracking of fossil fuels (40). The majority of carbon monoxide is produced as a component of syngas through coal gasification or steam methane reforming (41). Ethanol is primarily produced through fermentation of sugars or corn (42). Formic acid is primarily produced through chemical processes using tertiary amines (43). We find that when using optimistic targets (electricity cost = 4 cents/kWh, Faradaic efficiency = 90%, energy conversion efficiency = 70%), electrocatalysis is cost-competitive with fossil fuel–derived sources and more economical than biocatalytic processes. We nonetheless note that whereas fossil fuel–derived chemical production processes are well established, advances in biocatalytic processes have the potential to steadily drive down production costs and carbon emissions. For example, the U.S. Department of Energy has set the goal of biofuel production cost at $1 per gasoline gallon equivalent (currently $2.68/gge) with greenhouse gas reductions of 50% by 2020 (44).
为了对这些结果进行基准测试，我们比较了乙烯、一氧化碳、乙醇和甲酸生产的电催化、生物催化和传统化石燃料衍生工艺（表2）。在巴西，使用生物乙醇前体的生物乙烯生产在经济上具有竞争力，因为有充足的廉价甘蔗原料（39）。石化乙烯主要由化石燃料的蒸汽裂解生产（40）。大部分一氧化碳是通过煤气化或蒸汽甲烷重整作为合成气的组成部分产生的（41）。乙醇主要通过糖或玉米的发酵产生（42）。甲酸主要通过使用叔胺的化学过程生产 （43）。我们发现，当使用乐观的目标（电力成本 = 4 美分/千瓦时，法拉第效率 = 90%，能源转换效率 = 70%）时，电催化与化石燃料衍生来源相比具有成本竞争力，并且比生物催化过程更经济。尽管如此，我们注意到，虽然化石燃料衍生的化学生产工艺已经成熟，但生物催化工艺的进步有可能稳步降低生产成本和碳排放。例如，美国能源部将生物燃料生产成本设定为每加仑汽油当量1美元（目前为2.68美元/gge），到2020年温室气体减少50%（44）。

With these targets in mind, we now outline electrocatalysis as a means for the sustainable production of alcohols, olefins, and syngas.
考虑到这些目标，我们现在将电催化作为可持续生产醇类、烯烃和合成气的一种手段。

Among the various oxygenates that can be produced directly from electrochemical CO₂R or through sequential reaction pathways, alcohols are attractive for their utility as chemical precursors, drop-in fuels, and solvents. The global market for alcohols is in excess of $75 billion (45), which suggests that sustainable pathways toward methanol and higher (C2+) alcohols could provide alternative environmentally friendly routes to these high-demand products. Methanol is primarily synthesized through circuitous oxidation and reduction processes, by first reforming natural gas sources to syngas and converting this reaction mixture (46). A few recent studies have reported high selectivity for direct CO₂R to methanol (47–49), and further evaluation may yield valuable design principles for electrocatalytic systems that can accomplish a direct synthesis. Alternatively, a number of recent studies have reported high selectivity for direct CO₂R and carbon monoxide reduction (COR) to ethanol, and lower but non-negligible selectivity to n-propanol (50–55).
在可直接由电化学 CO ₂ R 或通过顺序反应途径产生的各种含氧化合物中，醇因其作为化学前体、即插即用燃料和溶剂的效用而具有吸引力。全球醇类市场超过750亿美元（45），这表明通往甲醇和更高（C2+）醇类的可持续途径可以为这些高需求产品提供替代的环保途径。甲醇主要通过迂回氧化和还原过程合成，首先将天然气源重整为合成气并转化这种反应混合物 （46）。最近的一些研究报道了直接将 CO ₂ R 转化为甲醇的高选择性 （47–49），进一步的评估可能会为能够完成直接合成的电催化系统提供有价值的设计原则。另外，最近的一些研究报道了直接将 CO ₂ R 和一氧化碳还原 （COR） 到乙醇的选择性很高，而对正丙醇的选择性较低但不可忽略 （50–55）。

Traditionally, higher alcohols are predominantly made through the fermentation of sugars (42, 56) or conversion of petrochemicals (57). The food versus fuel dilemma is still a long-standing social issue for the fermentation of foods or feeds. Biocatalysis is highly selective at making C2+ products and alcohols, but the economics of this process are dependent on the cost of sugar for fermentation. Production rates from biocatalysis are typically slower, water-intensive, and highly sensitive to the overall health of the microorganisms. Important advances have been made toward improving these processes in recent years, and progress is expected to continue.
传统上，高级醇主要通过糖的发酵（42,56）或石化产品（57）的转化制成。对于食品或饲料的发酵来说，食物与燃料的困境仍然是一个长期存在的社会问题。生物催化在制造 C2+ 产品和醇类方面具有高度选择性，但该过程的经济性取决于发酵糖的成本。生物催化的生产速度通常较慢，耗水量大，并且对微生物的整体健康状况高度敏感。近年来，在改进这些流程方面取得了重要进展，预计还会继续取得进展。

Direct synthesis of higher alcohols from syngas is a desirable alternative for both environmental and economic reasons. However, there are currently no thermochemical catalysts with the appropriate performance for industrial implementation of higher alcohol synthesis from syngas, motivating continued research in this area (57).
出于环境和经济原因，从合成气中直接合成高级醇是一种理想的替代方案。然而，目前还没有具有适当性能的热化学催化剂，可以工业化地从合成气中合成高醇，这激发了该领域的持续研究（57）。

Electrocatalysis has the advantage of productivity with a modular and scalable approach to producing small C1 to C3 molecules and H₂. Although some of these electrocatalytic technologies are still in the development stage, the already promising selectivity indicates that there may be intrinsic advantages to electrochemical processes for the synthesis of methanol and higher alcohols, although product separation remains a challenge. While there is clearly potential for electrochemical CO₂R and/or COR technologies to have a large impact on global alcohol industries, we note that many alcohols such as methanol and ethanol (Table 2) can be produced at costs of <$1/kg through current industrial processes (58). Therefore, market penetration will be initially (and possibly continually) very difficult, except in specialized applications that may need the flexibility of modular reactors.
电催化具有生产率的优势，采用模块化和可扩展的方法来生产小的 C1 至 C3 分子和 H ₂ 。尽管其中一些电催化技术仍处于开发阶段，但已经很有希望的选择性表明，尽管产物分离仍然是一个挑战，但电化学过程在合成甲醇和高级醇方面可能具有内在优势。虽然电化学CO ₂ R和/或COR技术显然有可能对全球酒精行业产生重大影响，但我们注意到，通过当前的工业流程，许多醇类，如甲醇和乙醇（表2）可以以<1美元/千克的成本生产（58）。因此，市场渗透最初（并可能持续）非常困难，除非在可能需要模块化反应堆灵活性的专业应用中。

Ethylene is produced at an annual rate of 150 Mt/year globally, the most of any organic chemical compound. It is a versatile building block used in the petrochemical industry. The majority of ethylene is used as a chemical intermediate for the preparation of some of the world’s most heavily used plastics, including polyethylene (116 Mt/year), polyvinyl chloride (38 Mt/year), and polystyrene (25 Mt/year) (40); the compound is also used for the production of antifreeze and detergents, and in the agricultural sector as a fruit ripener. Ethylene has traditionally been produced by energy-intensive steam cracking of naphtha obtained from crude oil; however, in recent years the shale gas boom has led to an abundance of inexpensive feedstocks that have spurred capital investment in the United States to build many new ethane crackers or retrofit existing steam cracking facilities to accommodate light gas feeds (59).
乙烯的全球年产量为150吨/年，是所有有机化合物中产量最高的。它是石化工业中使用的多功能构建块。大多数乙烯被用作化学中间体，用于制备世界上一些使用最频繁的塑料，包括聚乙烯（116 Mt/年）、聚氯乙烯（38 Mt/年）和聚苯乙烯（25 Mt/年）（40）;该化合物还用于生产防冻剂和洗涤剂，并在农业领域用作水果成熟剂。传统上，乙烯是通过从原油中获得的石脑油的能源密集型蒸汽裂解来生产的;然而，近年来，页岩气的繁荣导致了大量廉价的原料，刺激了美国的资本投资，以建造许多新的乙烷裂解装置或改造现有的蒸汽裂解设施以适应轻质天然气进料（59）。

Ethylene is a prime example of a petrochemical commodity priced on feedstock cost and consistency of supply. In North America, where ethylene is primarily produced from cracking of inexpensive and abundant ethane from shale gas reserves, prices can be as low as $250/tonne. However, in regions such as Europe and Asia where naphtha is the main feedstock, ethylene cost can be as high as $1200/tonne (60). In these regions, where the price of the feedstock is volatile, electrocatalytic conversion may have a greater chance of gaining a foothold on the market.
乙烯是石化商品的一个典型例子，它以原料成本和供应的一致性为定价。在北美，乙烯主要通过从页岩气储量中裂解廉价而丰富的乙烷来生产，价格可能低至250美元/吨。然而，在以石脑油为主要原料的欧洲和亚洲等地区，乙烯成本可能高达1200美元/吨（60）。在这些原料价格波动较大的地区，电催化转化可能有更大的机会在市场上站稳脚跟。

Although alternative routes for ethylene production are under development, including catalytic dehydrogenation of light alkanes, Fischer-Tropsch (FT) synthesis, or oxidative coupling of methane, these processes each rely on fossil fuel feedstocks and remain uneconomical or require further development. The development of catalysts and reactor designs that can simultaneously achieve high energy efficiencies, selectivity, high conversion rates, and long-term operational durability is the key outstanding challenge in this field. Over the past several years, many advances have contributed to a deeper fundamental understanding of electrochemical CO₂ reduction, such as the impact that the electrolyte [pH (61, 62), ions (63, 64), additives (65)], surface structure (66–69), and alloying (70) can have on copper catalyst activity and selectivity toward C-C coupled products such as ethylene. Only more recently has this knowledge been translated to practical flow-cell CO₂ reduction devices that have attained current densities on the order of >100 mA/cm² toward ethylene (61, 71).
尽管乙烯生产的替代途径正在开发中，包括轻烷烃的催化脱氢、费托 （FT） 合成或甲烷的氧化偶联，但这些工艺都依赖于化石燃料原料，仍然不经济或需要进一步开发。开发能够同时实现高能效、选择性、高转化率和长期运行耐久性的催化剂和反应器设计是该领域的主要突出挑战。在过去的几年中，许多进展有助于更深入地了解电化学CO ₂ 还原，例如电解质[pH值（61,62），离子（63,64），添加剂（65）]，表面结构（66-69）和合金化（70）对铜催化剂活性和对C-C偶联产物（如乙烯）的选择性的影响。直到最近，这些知识才被转化为实际的流通池CO ₂ 还原装置，这些装置的电流密度约为>100 mA / cm ² ，相对于乙烯（61,71）。

One possible use of electrochemical CO₂ conversion is the sustainable production of ethylene and polyethylene. In this case, post-consumer plastic could be recycled by incineration where energy (heat) capture (72) could ideally be coupled with electrochemical reduction of the combustion products (CO₂) to close the carbon cycle. This could mitigate plastic waste accumulation in landfills or in the environment, which is estimated at more than 4900 Mt and counting (40), and ultimately could provide a pathway for converting polyethylene back into sustainable ethylene at the end of its useful lifetime. Electrocatalysis could enable the production of ethylene from CO₂ emissions and/or from post-consumer plastic, rather than from fossil feedstocks, resulting in different economics than in the established petrochemical industry.
电化学一氧化碳 ₂ 转化的一种可能用途是乙烯和聚乙烯的可持续生产。在这种情况下，消费后塑料可以通过焚烧回收，其中能量（热）捕获（72）可以理想地与燃烧产物（CO ₂ ）的电化学还原相结合，以关闭碳循环。这可以减少垃圾填埋场或环境中的塑料废物堆积，估计超过4900公吨，并且还在增加（40），并最终可以提供一条途径，将聚乙烯在其使用寿命结束时转化为可持续乙烯。电催化可以使乙烯的生产能够从二氧化碳 ₂ 排放和/或消费后塑料中生产乙烯，而不是从化石原料中生产乙烯，从而产生与现有石化行业不同的经济效益。

There exist many sequential reaction pathways for converting CO₂ to chemicals and fuels, such as single- (C1) or multi-carbon (C2+) oxygenates and hydrocarbons. Leveraging these reaction sequences, one approach is to first convert CO₂ into stable intermediate species that can be further upgraded to the desired product(s) using biocatalysts such as enzymes and bacteria.
将一氧化碳 ₂ 转化为化学品和燃料存在许多顺序反应途径，例如单碳（C1）或多碳（C2+）含氧化合物和碳氢化合物。利用这些反应序列，一种方法是首先将一氧化碳 ₂ 转化为稳定的中间物质，这些中间物质可以使用酶和细菌等生物催化剂进一步升级为所需产物。

Among suitable reaction intermediates, CO stands out as it is a common gaseous precursor for numerous thermochemical, biological, and electrochemical processes. Mixtures of CO with H₂ (syngas) can serve as feedstocks for FT (73) synthesis or fermentation (74, 75) processes that are implemented today. For example, FT production of diesel is an industrially mature process with plants producing 11.5 tonnes/day, an energy conversion efficiency of 51%, and greenhouse gas emissions of 3.8 tonnes CO₂/tonne product, resulting in diesel costs of $240 to $525/tonne (76). Biocatalytic syngas fermentation with enzymes and bacteria can produce more valuable chemicals such as acetic acid, butyric acid, ethanol, butanol, and biodegradable polymers such as polyhydroxyalkanoates (PHAs). For a 1 tonne/year production facility with a biocatalytic syngas conversion of 90% and emissions of 0.26 to 0.45 tonnes CO₂/tonne product, the cost of PHA production is $1650/tonne (77, 78). The contrast between these two syngas utilization routes highlights the advantages and challenges of biocatalytic versus FT routes. FT synthesis operates at much higher rates of production and is less expensive for fuel production but has greater carbon emissions, whereas biocatalytic routes operate at lower volume, produce fewer emissions, and target more expensive specialty chemicals. Integrating electrocatalytic and biocatalytic process in the short term represents a promising approach due to the matching of production rates and higher value of the end product.
在合适的反应中间体中，一氧化碳脱颖而出，因为它是许多热化学、生物和电化学过程的常见气态前体。CO 与 H ₂ （合成气）的混合物可用作今天实施的 FT （73） 合成或发酵 （74， 75） 过程的原料。例如，FT柴油生产是一个工业成熟的过程，工厂每天生产11.5吨，能源转换效率为51%，温室气体排放量为3.8吨CO ₂ /吨产品，导致柴油成本为240美元至525美元/吨（76）。用酶和细菌进行生物催化合成气发酵可以产生更有价值的化学物质，如乙酸、丁酸、乙醇、丁醇和可生物降解的聚合物，如聚羟基链烷酸酯（PHA）。对于生物催化合成气转化率为90%，排放量为0.26至0.45吨CO ₂ /吨产品的1吨/年生产设施，PHA生产成本为1650美元/吨（77,78）。这两种合成气利用路线之间的对比突出了生物催化与FT路线的优势和挑战。FT合成的生产率要高得多，燃料生产成本更低，但碳排放量更大，而生物催化路线的产量更低，排放更少，并且针对更昂贵的特种化学品。在短期内将电催化和生物催化工艺相结合是一种很有前途的方法，因为它的生产率和最终产品的更高价值相匹配。

The syngas precursors used in conventional industrial processes are almost exclusively produced by steam methane reforming that, depending on the method, can co-generate different molar ratios of CO and H₂ (79). Although these processes are relatively cost-effective and extensive process optimization has been applied to minimize greenhouse gas emissions, the exclusive reliance on fossil fuel sources motivates the development of more sustainable syngas production pathways.
传统工业过程中使用的合成气前驱体几乎完全由蒸汽甲烷重整生产，根据方法的不同，可以共产生不同的 CO 和 H 摩尔比 ₂ （79）。尽管这些工艺相对具有成本效益，并且已经应用了广泛的工艺优化以最大限度地减少温室气体排放，但对化石燃料来源的完全依赖促使了更可持续的合成气生产途径的发展。

One such sustainable pathway to CO is electrochemical CO₂R, where ideally a high-yield near-ambient process could generate a stream of CO from CO₂, H₂O, and electricity. Because CO is gaseous under ambient conditions, a selective CO₂R process would enable direct CO evolution and downstream use from an aqueous electrolyzer device. In the case of syngas, H₂ production is complementary and not parasitic to CO₂R, allowing for co-generation because HER and CO₂R have comparable half-cell potentials under nearly identical electrochemical conditions. Although syngas production from CO₂ electrolysis with controlled CO:H₂ ratios is possible (80), technoeconomic analysis favors the highest possible selectivity to CO, which is the more valuable product (33). Co-generation of CO and H₂ could nonetheless be advantageous for situations where it is essential to have on-site and on-demand syngas production from a single reactor (81).
其中一种可持续的一氧化碳途径是电化学一氧化 ₂ 碳，理想情况下，高产率的近环境工艺可以从一氧化碳 ₂ 、氢 ₂ 氧化物和电力中产生一氧化碳流。由于 CO 在环境条件下是气态的，因此选择性 CO ₂ R 工艺将实现 CO 的直接释放和水性电解槽装置的下游使用。在合成气的情况下，H ₂ 的产生是互补的，而不是寄生在CO ₂ R上，允许热电联产，因为HER和CO ₂ R在几乎相同的电化学条件下具有相当的半电池电位。尽管在CO：H ₂ 比受控的情况下，CO ₂ 电解可以生产合成气（80），但技术经济分析倾向于对CO具有尽可能高的选择性，而CO是更有价值的产品（33）。尽管如此，CO和H ₂ 的热电联产对于必须从单个反应器进行现场和按需合成气生产的情况可能是有利的（81）。

To date, electrochemical CO₂R has been demonstrated with high selectivity and/or reaction rates to CO and syngas in CO₂ electrolyzers (80–84). A recent breakthrough in this area was achieved by a collaboration of Siemens, Covestro, and Evonik. The team demonstrated a system whereby solar-powered electrochemical reduction of CO₂ into syngas was followed by fermentation with bacteria to selectively produce butanol or hexanol, depending on the type of anaerobic digester used (81). Stable CO₂ reduction was carried out at industrially relevant current densities (300 mA cm⁻²) with near 100% Faradaic efficiency for syngas (CO + H₂). Following this applied advance, Siemens and Evonik recently announced a plan to build a test plant with the goal of 20,000 tonnes of annual production capacity for butanol and hexanol (85).
迄今为止，电化学 CO ₂ R 已被证明对 CO ₂ 电解槽中的 CO 和合成气具有高选择性和/或反应速率 （80–84）。西门子、科思创和赢创的合作在这一领域取得了最近的突破。该团队展示了一种系统，该系统将太阳能电化学还原 ₂ 为合成气，然后用细菌发酵以选择性地产生丁醇或己醇，具体取决于所使用的厌氧消化器的类型（81）。在工业相关的电流密度（300 mA cm ⁻² ）下，合成气（CO + H）的法拉第效率接近100%，实现了稳定的CO ₂ 还原 ₂ 。随着这一应用的进步，西门子和赢创最近宣布了一项计划，计划建立一个测试工厂，目标是年产20,000吨丁醇和己醇（85）。

This example presents an exciting future avenue for commodity chemical production: the coupling of biocatalytic processes with electrocatalytic processes (Fig. 4). There has been some initial promising work in this area, interfacing biological systems with inorganic systems for solar fuels and fertilizer production (86, 87). The current state of the art couples water-splitting electrocatalysts with engineered bacteria to convert CO₂ into polymers and alcohols (88, 89) or nitrogen into ammonia (90). These efforts have focused mainly on the electrochemical production of H₂ or acetate as input for bacteria (87, 91).
这个例子为商品化学品生产提供了一个令人兴奋的未来途径：生物催化过程与电催化过程的耦合（图4）。在这一领域已经有一些初步的有希望的工作，将生物系统与用于太阳能燃料和肥料生产的无机系统连接起来（86,87）。目前最先进的技术是将水分解电催化剂与工程细菌相结合，将CO ₂ 转化为聚合物和醇（88,89）或将氮转化为氨（90）。这些努力主要集中在H ₂ 或乙酸盐的电化学生产上，作为细菌的输入（87,91）。

Although we have chosen to highlight CO as a promising intermediate, we also note that there are other possible sequential reaction pathways from the myriad of oxygenated intermediates that can be produced from CO₂R. Other commonly observed oxygenates from electrochemical CO₂R, such as formate, can be used as the sole carbon source for microorganisms or enzymes to selectively upgrade into the desired oxygenates and hydrocarbons (92, 93).
尽管我们选择强调 CO 是一种很有前途的中间体，但我们也注意到，从 CO ₂ R 可以产生的无数含氧中间体中还有其他可能的顺序反应途径。来自电化学CO ₂ R的其它常见观察到的含氧化合物，如甲酸盐，可以用作微生物或酶的唯一碳源，以选择性地升级为所需的含氧化合物和碳氢化合物（92,93）。

The field of electrocatalysis, especially with copper-based catalysts, has recently been focusing on engineering catalysts to make one specific high-value product as selectively as possible. This approach lowers the product separation costs and makes the overall process more economical. One opportunity for the biocatalytic community will be to engineer microorganisms that can tolerate the electrolyte and a diverse CO₂R liquid product mix (Fig. 4). If engineered microorganisms can be used to process a less selective input mix from CO₂R (ethanol, acetate, formate, methanol) and then upgrade the combined feedstocks into higher-value commodity chemicals, then electrocatalytic selectivity and energy-intensive separation processes would no longer be a limiting constraint. High-production electrocatalysis combined with highly selective biocatalysis may offer a practical pathway to combine integrated renewable energy production with chemicals manufacturing.
电催化领域，特别是铜基催化剂，最近一直专注于工程催化剂，以尽可能选择性地制造一种特定的高价值产品。这种方法降低了产品分离成本，使整个过程更加经济。生物催化界的一个机会是设计能够耐受电解质和多样化 CO ₂ R 液体产品混合物的微生物（图 4）。如果工程微生物可用于处理来自CO ₂ R（乙醇、乙酸盐、甲酸盐、甲醇）的选择性较低的输入混合物，然后将组合的原料升级为更高价值的商品化学品，那么电催化选择性和能源密集型分离过程将不再是一个限制性限制。高产电催化与高选择性生物催化相结合，可以为将可再生能源生产与化学品制造相结合提供一条实用的途径。

Even with recent progress, there exist technological challenges and market entry barriers that need to be overcome for electrosynthesis of commodity chemicals to become industrially competitive. From a technical standpoint, scientific research has focused largely on aqueous CO₂R systems that are limited as a result of the solubility of CO₂ in water. To address this issue, there has been a push toward flow-cell and gas diffusion–type architectures that operate at more industrially relevant current densities (>100 mA/cm²) (58, 94). Continued research on high-current density electrolyzer architectures is needed to increase the energy conversion efficiency. Product separation is another technical cost that needs to be addressed (95). For example, in petrochemical ethylene production, the cryogenic separation of ethylene and ethane is capital-intensive (~50% of capital) and consumes a large amount of energy (96). Electrochemical CO₂R does not produce ethane, thereby avoiding expensive cryogenic separation. Instead, membrane-based porous materials for ethylene separation have recently achieved high selectivity, indicating progress toward lower-cost, more efficient separation processes (97) that could potentially be used for product separation from CO₂R. Furthermore, the technology developed for carbon capture materials (98) could also be used for separation of unreacted CO₂ from ethylene (an easier separation than olefin/paraffin separations) in the output stream. Recent work on optimizing single-pass conversion at high selectivity (99) also shows promise in reducing separation costs downstream. It should be noted that there is very limited durability data of CO₂ electrolyzers, as this field is still nascent. Another technical challenge will be to show operating stability over thousands of hours for this technology to be economical.
即使最近取得了进展，也存在技术挑战和市场进入壁垒，需要克服这些挑战和市场进入壁垒，才能使商品化学品的电合成具有工业竞争力。从技术角度来看，科学研究主要集中在水性CO ₂ R系统上，由于CO ₂ 在水中的溶解度而受到限制。为了解决这个问题，人们一直在推动流通池和气体扩散型架构，这些架构在更工业相关的电流密度（>100 mA / cm ² ）下运行（58,94）。需要继续研究高电流密度电解槽架构，以提高能量转换效率。产品分离是另一个需要解决的技术成本（95）。例如，在石化乙烯生产中，乙烯和乙烷的低温分离是资本密集型的（~50%的资本）并且消耗大量能源（96）。电化学CO ₂ R不产生乙烷，从而避免了昂贵的低温分离。相反，用于乙烯分离的膜基多孔材料最近实现了高选择性，表明在更低成本、更高效的分离工艺（97）方面取得了进展，该工艺可能用于从CO ₂ R中分离产物。此外，为碳捕获材料开发的技术（98）也可用于在输出流中 ₂ 从乙烯中分离未反应的一氧化碳（比烯烃/石蜡分离更容易分离）。最近在高选择性（99）下优化单程转化的工作也显示出降低下游分离成本的希望。应该注意的是，一氧化碳 ₂ 电解槽的耐久性数据非常有限，因为该领域仍处于起步阶段。 另一个技术挑战是展示数千小时的运行稳定性，以使该技术具有经济性。

An additional technical challenge is the need for chemical plants to run continually for both capital efficiency and process safety, highlighting the need for nonintermittent electricity. If an electrochemical plant operates continuously, then its capital utilization is 100% (loading factor), and the system does not require design for time-varying biases. However, renewable baseloads typically command higher electricity market prices, because they are in effect dispatchable. On the other hand, if an electrochemical plant is to use low-cost intermittent renewable electricity (e.g., solar with a typical capacity factor of 0.22), the contribution of capital cost is increased (fig. S2) and the system must tolerate drastic swings (including to unbiased conditions) in driving voltage. As seen in fig. S2, because capital cost is expected to play a notable but not dominant role in total renewable chemicals cost, reducing the capacity factor from 1 to 0.22 leads to a 20% increase in chemicals cost. Hydroelectric and geothermal power plants are examples of renewable baseloads that may mitigate this risk. Additionally, greater advances in lowering the capital expenditure costs could potentially sustain lower capacity factors. Finally, lower costs of grid-scale energy storage, driven by the decrease in cost of Li-ion technology, are bringing hour-by-hour storage within reason, and future lower-cost grid-scale batteries could further enable electrochemical processes as well.
另一个技术挑战是化工厂需要持续运行，以确保资本效率和工艺安全，这凸显了对非间歇性电力的需求。如果电化学工厂连续运行，则其资本利用率为100%（加载因子），并且系统不需要针对时变偏差进行设计。然而，可再生能源基荷通常要求更高的电力市场价格，因为它们实际上是可调度的。另一方面，如果电化学工厂要使用低成本的间歇性可再生电力（例如，典型容量系数为 0.22 的太阳能），则资本成本的贡献会增加（图 S2），并且系统必须能够承受驱动电压的剧烈波动（包括无偏置条件）。如图所示。S2，由于资本成本预计将在可再生化学品总成本中发挥显著但不是主导作用，因此将容量系数从 1 降低到 0.22 会导致化学品成本增加 20%。水力发电厂和地热发电厂是可再生基荷的例子，可以减轻这种风险。此外，在降低资本支出成本方面取得更大进展可能会维持较低的产能系数。最后，在锂离子技术成本降低的推动下，电网规模储能成本的降低使每小时的储能成为合理的范围，未来低成本的电网规模电池也可以进一步实现电化学过程。

The manufacturing scale and installed capacity for commodity chemicals such as ethylene also present barriers for a new technology to penetrate these saturated, complex, and capital-intensive markets. The case can be made for electrochemical technologies to supplement existing fossil fuel processes by retrofitting existing plants, thereby decreasing the financial burden of shutting down expensive existing assets. Retrofitting power plants carries a nontrivial capital cost but has been already been successfully demonstrated with post-combustion carbon capture technologies (100). Electrochemical technologies may also provide lower cost to add chemical production capacity going forward, supplementing the existing industry as the market continues to grow. Furthermore, electrochemical production costs are dependent mainly on the price of electricity, providing a more stable feedstock price than naphtha feedstocks that are more sensitive to price fluctuations. Ultimately, a focus on C-C bond formation and subsequent C2+ products provides a technological basis to target higher-value chemicals. The source and costs of renewable electricity are another factor to consider when discussing scale (see Fig. 2 and fig. S1). Electrocatalytic technology may find a source of cheap electricity from areas with excess hydroelectric capacity, such as northeastern Canada. Transportation costs between large CO₂ emitters and C2 and C3 production facilities are also another challenge, although we note that petrochemical plants for C2 and C3 production are in themselves point sources of CO₂ emissions. For example, the NOVA Chemicals Joffre petrochemical plant in Alberta is the 15th largest industrial CO₂ point source in Canada, emitting >3 Mt of CO₂ in 2016 (101). In Canada, the petrochemical industry is located in three main clusters near Calgary, Sarnia (Ontario), and Montreal. CO₂ point sources in the Alberta oil sands are colocated with the petrochemical plants, whereas CO₂ point sources from Canadian manufacturing, cement, and steel mills in Ontario are also located near Sarnia. However, not all C2 and C3 production sites are located near CO₂ point sources. The cost of CO₂ transportation is estimated to be $10/tonne CO₂ for 200 km, rising to $44/tonne for 12,000 km (102).
乙烯等大宗化学品的制造规模和装机容量也为新技术渗透这些饱和、复杂和资本密集型市场提供了障碍。电化学技术可以通过改造现有工厂来补充现有的化石燃料工艺，从而减轻关闭昂贵现有资产的财务负担。改造发电厂的资本成本不小，但已经成功地通过燃烧后碳捕获技术进行了证明（100）。随着市场的持续增长，电化学技术还可以提供更低的成本来增加化学生产能力，补充现有行业。此外，电化学生产成本主要取决于电价，与对价格波动更敏感的石脑油原料相比，电化学生产成本提供了更稳定的原料价格。最终，专注于 C-C 键的形成和后续的 C2+ 产品为靶向更高价值的化学品提供了技术基础。在讨论规模时，可再生电力的来源和成本是另一个需要考虑的因素（见图2和图S1）。电催化技术可能会从水力发电能力过剩的地区（例如加拿大东北部）找到廉价电力来源。大型一氧化碳 ₂ 排放者与 C2 和 C3 生产设施之间的运输成本也是另一个挑战，尽管我们注意到用于生产 C2 和 C3 的石化厂本身就是一氧化碳 ₂ 排放的点源。 例如，阿尔伯塔省的 NOVA Chemicals Joffre 石化厂是加拿大第 15 大工业一氧化碳 ₂ 点源， ₂ 2016 年排放 >3 公吨一氧化碳 （101）。在加拿大，石化行业位于卡尔加里、萨尼亚（安大略省）和蒙特利尔附近的三个主要集群。阿尔伯塔省油砂中的一氧化碳 _{2 2} 点源与石化厂位于同一地点，而来自安大略省加拿大制造业、水泥厂和钢铁厂的一氧化碳点源也位于萨尼亚附近。然而，并非所有 C2 和 C3 生产基地都位于 CO ₂ 点源附近。一氧化碳 ₂ 运输成本估计 ₂ 为200公里10美元/吨一氧化碳，12,000公里上升至44美元/吨（102）。

Another consideration is future societal acceptability. As the consequences of climate change grow more severe, governments and the public will demand more of the private sector to cut emissions and decarbonize. The economic argument presented here is based on pure cost of production and does not include carbon pricing schemes or the demands of shareholders on large carbon emitters. For example, in 2018 there were 53 carbon pricing initiatives worldwide that covered 11 Gt CO₂e, representing 19.8% of global greenhouse gas emissions (103). The total value of carbon pricing initiatives was valued at $82 billion in 2018, and these initiatives are only continuing to grow, enhancing the economic case for electroconversion of CO₂.
另一个考虑因素是未来的社会接受度。随着气候变化的后果越来越严重，政府和公众将要求更多的私营部门减少排放和脱碳。这里提出的经济论点是基于纯粹的生产成本，不包括碳定价计划或股东对大型碳排放者的要求。例如，2018 年，全球有 53 项碳定价倡议，涵盖 11 Gt CO ₂ e，占全球温室气体排放量的 19.8%（103）。2018 年，碳定价计划的总价值为 820 亿美元，而且这些计划只会继续增长，从而增强了 CO 电转换的经济案例 ₂ 。

Finally, there is an open question of how feedstock needs may change in the future, and how future electrolyzer technologies will fit in, beyond competing head-to-head against the current paradigm as discussed above. As technologies are advanced in all sectors simultaneously, the needs of future society will evolve as well. For instance, R&D efforts in using carbon as a building material could lead to a future where carbon replaces a large proportion of steel and cement, two industries with remarkably large CO₂ footprints. Electrolyzer technologies that readily convert CO₂ into carbon using low-carbon electricity would naturally dovetail with such a future building industry, allowing for sustainably produced building materials provided on-site at the point of construction.
最后，还有一个悬而未决的问题，即未来原料需求将如何变化，以及未来的电解槽技术将如何适应，而不是与上面讨论的当前范式进行正面竞争。随着各行各业的技术同步进步，未来社会的需求也将不断发展。例如，使用碳作为建筑材料的研发工作可能会导致碳取代钢铁和水泥的很大一部分，这两个行业的二氧化碳 ₂ 足迹非常大。使用低碳电力将一氧化碳 ₂ 转化为碳的电解槽技术自然会与未来的建筑业相吻合，从而允许在施工现场提供可持续生产的建筑材料。

The transformation of the chemical production industry to emissions-free processes will rely on a variety of technologies working in combination. Electrocatalysis can be implemented throughout the chemical supply chain and could include electrosynthesis of basic building blocks, higher-value fine chemicals in combination with biocatalytic processes, and supplementation of traditional thermocatalysis pathways. The economics of electrocatalytic processes will be highly dependent on the availability and price of renewable electricity, the regional cost of feedstock and of traditional petrochemical manufacture, the maturity of carbon capture technologies, and the social, political, and economic incentives to transition to low-carbon processes.
化工生产行业向零排放工艺的转型将依赖于各种技术的结合。电催化可以在整个化学品供应链中实施，可能包括基本构件的电合成、与生物催化工艺相结合的高价值精细化学品以及补充传统热催化途径。电催化工艺的经济性将在很大程度上取决于可再生电力的可用性和价格、原料和传统石化制造的区域成本、碳捕获技术的成熟度以及向低碳工艺过渡的社会、政治和经济激励措施。

As electrochemical technologies mature and our knowledge of transforming small, abundant molecules deepens, the possibilities of producing renewable chemicals will multiply. Hydrogen electrolyzers represent the first generation of these clean fuel technologies; CO₂ electrolyzers are poised to be the second generation for production of fuels and chemicals, and the nascent field of N₂ reduction to ammonia may represent the future of renewable fertilizer production.
随着电化学技术的成熟和我们对转化小而丰富的分子的了解的加深，生产可再生化学品的可能性将成倍增加。氢电解槽代表了这些清洁燃料技术的第一代;一氧化碳 ₂ 电解槽有望成为生产燃料和化学品的第二代产品，而氮 ₂ 还原为氨的新兴领域可能代表了可再生肥料生产的未来。

There still remain many scientific and engineering challenges for this technology to truly penetrate the petrochemical market, but the advances in recent years suggest that these challenges can be overcome. As society evolves with new paradigms of operation, continued market opportunities will likely emerge. Regardless of the technical challenges, considerable economic barriers also exist within the complex, established, and highly connected petrochemical industry. Despite these challenges, the adoption and growth of renewable energy technologies such as solar and wind provide a promising pathway to follow.
这项技术要真正渗透到石化市场，仍然存在许多科学和工程挑战，但近年来的进步表明，这些挑战是可以克服的。随着社会以新的运营模式发展，可能会出现持续的市场机会。尽管存在技术挑战，但在复杂、成熟且高度关联的石化行业中也存在相当大的经济障碍。尽管存在这些挑战，但太阳能和风能等可再生能源技术的采用和发展提供了一条有希望的途径。

P.D.L. thanks C.-T. Dinh for discussions and feedback on the economic model. The authors also thank B. Winter and A. Bardow for discussions and input on improving the carbon emissions model. Funding: This material is based on work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under award DE-SC0004993. This work was also supported by the Natural Sciences and Engineering Council of Canada. Author contributions: P.D.L., C.H., and D.H. wrote the manuscript and generated the figures; S.A.J., T.F.J., and E.H.S. supervised the work and provided edits to the manuscript. Competing interests: S.A.J. is the vice president of corporate science and technology projects at Total American Services, an affiliate of Total S.A., a French integrated energy company. P.D.L. and E.H.S. are currently finalists in the Carbon XPRIZE, funded by NRG and COSIA (Canada Oil Sands Innovation Alliance).
P.D.L. 感谢 C.-T.Dinh 对经济模型进行讨论和反馈。作者还感谢 B. Winter 和 A. Bardow 对改进碳排放模型的讨论和投入。资金：本材料基于人工光合作用联合中心（美国能源部能源创新中心）开展的工作，由美国能源部科学办公室根据 DE-SC0004993 奖励提供支持。这项工作也得到了加拿大自然科学与工程委员会的支持。作者贡献：P.D.L.、C.H. 和 D.H. 撰写了手稿并生成了图表;S.A.J.、T.F.J. 和 E.H.S. 监督了这项工作，并对手稿进行了编辑。利益争夺：S.A.J.是法国综合能源公司Total S.A.的附属公司Total American Services的企业科学和技术项目副总裁。P.D.L. 和 E.H.S. 目前是 Carbon XPRIZE 的决赛入围者，该奖项由 NRG 和 COSIA（加拿大油砂创新联盟）资助。