Discovery of an energy efficient and selective electrochemical CO2 reduction (CO2RR ) catalyst is the first and most important step in achieving a truly closed-loop carbon economy based on recycling CO2. Here, we introduce five, structurally distinct, nickel phosphide compounds as electrocatalysts for CO2RR, examining each as a function of potential in aqueous electrolyte. The best nickel phosphide catalyst exhibits a higher selectivity to C3 and C4 products than that observed on any other reported catalyst. At overpotentials as low as 10 mV, energy efficiency equal to 99% percent is achieved - which is unprecedented in the ambient and aqueous CO2 reduction literature. We propose a mechanism for the formation of multi-carbon products in which hydride transfer (surface *H-) initiates the reduction of CO2 at near-zero overpotentials. Hydride reaction mechanisms are commonly observed in CO2 reducing enzymes. This reaction mechanism produces higher molecular weight products than observed on simple metals, which react via atomic *H or individual proton+electron transfer steps. Three products are observed: formic acid (C1), methylglyoxal (C3), and 2,3-furandiol (C4) at potentials as low as +50 mV vs. RHE. The maximum faradaic (current) efficiency for 2,3-furandiol is 71% at 0.00 V vs. RHE on Ni2P, with methylglyoxal — a proposed reaction intermediate -— comprising the balance. This performance is dramatically different from the state-of-the-art metallic catalysts that have poorer selectivity and require greatly higher overpotentials (&gt;700 mV) to achieve significant reaction rates.

Nickel phosphides: A new family of catalysts for energy-efficient electrochemical CO2 reduction to C3 and C4 products

256th National Meeting (2018)

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