- Georg Kastlunger Technical University of Denmark ,
- Lei Wang Stanford University & National University of Singapore ,
- Nitish Govindarajan Technical University of Denmark ,
- Hendrik H. Heenen Technical University of Denmark & Fritz Haber Institute of the Max Planck Society ,
- Stefan Ringe Daegu Gyeongbuk Institute of Science and Technology ,
- Thomas Jaramillo Stanford University ,
- Christopher Hahn SLAC National Accelerator Laboratory & Lawrence Livermore National Laboratory ,
- Karen Chan Technical University of Denmark
Electrochemical conversion of CO(2) into hydrocarbons and oxygenates is envisioned as a promising path towards closing the carbon cycle in modern technology. To this day, however, the reaction mechanisms towards the plethora of products are disputed, complicating the search for novel catalyst materials. In order to conclusively identify the rate-limiting steps in CO reduction on Cu, we analyzed the mechanisms on the basis of constant potential DFT kinetics and experiments at a wide range of pH values (3 - 13). We find that *CO dimerization is energetically favoured as the rate limiting step towards multi-carbon products. This finding is consistent with our experiments, where the reaction rate is nearly unchanged on an SHE potential scale, even under acidic conditions. For methane, both theory and experiments indicate a change in the rate-limiting step with electrolyte pH from the first protonation step in acidic/neutral conditions to a later one in alkaline conditions. We also show, through a detailed analysis of the microkinetics, that a surface combination of *CO and *H is inconsistent with the measured current densities and Tafel slopes. Finally, we discuss the implications of our understanding for future mechanistic studies and catalyst design.
The experimental results are now directly compared to the measurements from a collection in the literature. The quality of the figures has been improved.