Solar production of fuels from CO2 with high efficiency and stability via in situ transformation of Bi electrocatalysts†

Abstract

The sustainable electrocatalytic reduction of carbon dioxide into solar fuels offers a potential pathway to mitigate the impact of greenhouse gas-induced climate change. Here, we successfully achieved a high solar-to-fuel (STF) efficiency of 11.5% by integrating a low-cost tandem solar cell with robust, high-performance, non-precious metal-based electrocatalysts. The bismuth-based cathode exhibited a high formic acid selectivity of 97.2% at a potential of −1.1 V_RHE, along with an outstanding partial current density of 32.5 mA cm⁻². Furthermore, upon undergoing more than 24 hours of electrolysis, we observed an enhancement in the catalytic activity. Through comprehensive analysis including in situ Raman spectroscopy and density functional theory (DFT) calculations, we elucidated that the in situ transformation of bismuth into bismuth subcarbonate (BOC) induces multiple effects: (i) the formation of grain boundaries between phases with distinct lattice parameters, (ii) electronic modulation due to defect formation, and (iii) changes in the binding modes of key reaction intermediates on active sites, resulting in the stabilization of *OCHO species. The cause of these phase transformations was attributed to the structural similarity between the cathode template and BOC. The sustainability of the STF efficiency sets a new benchmark for all cost-effective photovoltaic-coupled electrochemical systems.