Kauffman Douglas R, Thakkar Jay, Siva Rajan, Matranga Christopher, Ohodnicki Paul R, Zeng Chenjie, Jin Rongchao
†National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States.
‡Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
ACS Appl Mater Interfaces. 2015 Jul 22;7(28):15626-32. doi: 10.1021/acsami.5b04393. Epub 2015 Jul 10.
The catalytic conversion of CO2 into industrially relevant chemicals is one strategy for mitigating greenhouse gas emissions. Along these lines, electrochemical CO2 conversion technologies are attractive because they can operate with high reaction rates at ambient conditions. However, electrochemical systems require electricity, and CO2 conversion processes must integrate with carbon-free, renewable-energy sources to be viable on larger scales. We utilize Au25 nanoclusters as renewably powered CO2 conversion electrocatalysts with CO2 → CO reaction rates between 400 and 800 L of CO2 per gram of catalytic metal per hour and product selectivities between 80 and 95%. These performance metrics correspond to conversion rates approaching 0.8-1.6 kg of CO2 per gram of catalytic metal per hour. We also present data showing CO2 conversion rates and product selectivity strongly depend on catalyst loading. Optimized systems demonstrate stable operation and reaction turnover numbers (TONs) approaching 6 × 10(6) molCO2 molcatalyst(-1) during a multiday (36 h total hours) CO2 electrolysis experiment containing multiple start/stop cycles. TONs between 1 × 10(6) and 4 × 10(6) molCO2 molcatalyst(-1) were obtained when our system was powered by consumer-grade renewable-energy sources. Daytime photovoltaic-powered CO2 conversion was demonstrated for 12 h and we mimicked low-light or nighttime operation for 24 h with a solar-rechargeable battery. This proof-of-principle study provides some of the initial performance data necessary for assessing the scalability and technical viability of electrochemical CO2 conversion technologies. Specifically, we show the following: (1) all electrochemical CO2 conversion systems will produce a net increase in CO2 emissions if they do not integrate with renewable-energy sources, (2) catalyst loading vs activity trends can be used to tune process rates and product distributions, and (3) state-of-the-art renewable-energy technologies are sufficient to power larger-scale, tonne per day CO2 conversion systems.
将二氧化碳催化转化为具有工业价值的化学品是减少温室气体排放的一种策略。按照这些思路，电化学二氧化碳转化技术颇具吸引力，因为它们能够在环境条件下以高反应速率运行。然而，电化学系统需要电力，并且二氧化碳转化过程必须与无碳可再生能源相结合，才能在更大规模上可行。我们利用Au25纳米团簇作为可再生供电的二氧化碳转化电催化剂，其二氧化碳→一氧化碳的反应速率为每克催化金属每小时400至800升二氧化碳，产物选择性为80%至95%。这些性能指标对应于每克催化金属每小时接近0.8 - 1.6千克二氧化碳的转化率。我们还展示了数据，表明二氧化碳转化率和产物选择性强烈依赖于催化剂负载量。在包含多个启动/停止循环的为期多天（总计36小时）的二氧化碳电解实验中，优化后的系统展示出稳定运行且反应周转数（TONs）接近6×10⁶ molCO₂ mol催化剂⁻¹。当我们的系统由消费级可再生能源供电时，获得了1×10⁶至4×10⁶ molCO₂ mol催化剂⁻¹的TONs。实现了12小时的日间光伏供电二氧化碳转化，并使用太阳能可充电电池模拟了24小时的低光照或夜间运行。这项原理验证研究提供了评估电化学二氧化碳转化技术的可扩展性和技术可行性所需的一些初始性能数据。具体而言，我们表明：（1）如果所有电化学二氧化碳转化系统不与可再生能源相结合，将导致二氧化碳排放量净增加；（2）催化剂负载量与活性趋势可用于调整工艺速率和产物分布；（3）最先进的可再生能源技术足以支持每天处理吨级二氧化碳的大规模转化系统。
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