An experiment-guided descriptor framework for chain-growth CO2 electrocatalysis

The electroreduction of CO2 to long-chain hydrocarbons (LCHC) has been recently demonstrated on several transition metal-based catalysts. However, the properties of the catalysts that open this pathway have yet to be fully elucidated. Here, we combine experiments and modeling to establish a set of descriptors across a series of transition-metal based catalysts, which will serve as a general framework in determining the efficacy of a catalyst for generating LCHC. We first experimentally show that strong *CO-binding catalysts such as Ni, Co, Fe, Ru, Rh, and Pd drive chain-growth CO2 electrocatalysis toward LCHC. Hydrocarbon chain growth initiates from *CO formation and its hydrogenation to *CHx, followed by successive *CO insertion into a growing *RCHx chain. *CO hydrogenation and *CO-*CHx coupling are identified as the two key kinetic barriers governing chain growth. Guided by our experimental observations, density functional theory calculations were used to establish descriptors that rationalize LCHC formation. Unlike Cu (with moderate *CO binding) that favors *CO dimerization, strong *CO-binding catalysts favor *CO hydrogenation toward *CHx over *CO dimerization, thereby opening a route to LCHC. The relative barriers of *CO-*CHx coupling and the competing hydrogen evolution reaction further modulate LCHC yield. LCHC yield is further promoted by 3-7 fold across all catalysts by enhancing *CO hydrogenation under CO flow in a mildly acidic electrolyte. Overall, our results establish mechanistic descriptors and provide rational catalyst design principles for improving LCHC yield from CO2 electroreduction.