Bismuth nanosheets with rich grain boundaries for efficient electroreduction of CO2 to formate under high pressures

Electrochemical CO2 reduction reaction (CO2RR) driven by sustainable energy has emerged as an attractive route to achieve the target of carbon neutral. Formate is one of the most economically viable products, and electrocatalytic CO2RR to formate is a promising technology. High-pressure H-cell electrolyzer is easy to operate and allows high CO2 solubility for realizing high current density, but the design of highly efficient catalysts for working under high CO2 pressures remains challenging. Bismuth-based catalysts exhibit high formate selectivity, but suffer from limited activity. Here, we report a high-performance catalyst, which is derived from BiPO4 nanopolyhedrons during electrocatalytic CO2RR to formate in neutral solution under high CO2 pressures. A high partial current density of formate (534 mA cm−2) and formate formation rate (9.9 mmol h−1 cm−2) with a formate Faradaic efficiency of 90% have been achieved over BiPO4-derived catalyst at an applied potential of −0.81 V vs. RHE under 3.0 MPa CO2 pressure. We discover that BiPO4 nanopolyhedrons evolve into metallic Bi nanosheets with rich grain boundaries in electrocatalytic CO2RR under high CO2 pressures, and the grain boundaries of the BiPO4-derived catalyst play a vital role in promoting electrocatalytic CO2RR to formate. Our theoretical studies reveal that the charge redistribution occurs at the grain boundaries of Bi surface, and this promotes CO2 activation and increases HCOO* intermediate stability, thus making the pathway for CO2RR to formate more selective and energy-favorable. This work not only demonstrates a highly efficient catalyst for CO2RR to formate but also discovers a unique feature of catalyst evolution under high CO2 pressures.