title: Efficient electrochemical CO2 conversion powered by renewable energy.
abstract: 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.
authors.affiliation: †National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Kauffman
authors.affiliation: †National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States.
authors.forename: Jay
authors.initials: J
authors.lastname: Thakkar
authors.affiliation: †National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States.
authors.forename: Rajan
authors.initials: R
authors.lastname: Siva
authors.affiliation: †National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States.
authors.forename: Christopher
authors.initials: C
authors.lastname: Matranga
authors.affiliation: †National Energy Technology Laboratory, United States Department of Energy, Pittsburgh, Pennsylvania 15236, United States.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Ohodnicki
authors.affiliation: ‡Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Chenjie
authors.initials: C
authors.lastname: Zeng
authors.affiliation: ‡Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Rongchao
authors.initials: R
authors.lastname: Jin
keywords: CO2 conversion; catalysis; electrocatalysis; environmental; gold nanomaterials; renewable energy