Facet-engineered (003)-oriented Bi nanosheets for enhanced photoelectrocatalytic formate production

Photoelectrocatalytic CO₂ reduction reaction (PEC CO₂RR) offers a promising avenue for the direct and clean conversion of solar energy into chemical fuels. In this work, Bi nanosheets with highly active (003) facets were successfully deposited on p-Si by precisely tuning the concentration of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) in the electrodeposition solution. In the PEC CO₂RR reaction, the optimized photocathode exhibited high selectivity toward formate, with a Faradaic efficiency (FE) exceeding 80% over a wide potential range of -0.6 to -1.2 V vs. the reversible hydrogen electrode (RHE). The photoelectrode also demonstrated super stability, with both current density and product selectivity showing negligible decay during prolonged 10 h electrolysis. Critically, the introduction of the surfactant cetyltrimethylammonium bromide successfully suppressed the growth of the (003) facet in the electrodeposition process, resulting in a marked decrease in formate selectivity. This enhanced performance is attributed to the synergistic effects of the highly active (003) facet and the efficient photogenerated charge separation via the Schottky junction between Bi and p-Si. Besides, the introduction of a light field further increases the interfacial charge density and improves reaction kinetics at a lower overpotential. In situ infrared spectroscopy and density functional theory (DFT) calculations jointly confirm that the reaction proceeds via the critical *OCHO and *COOH intermediate pathway to efficiently produce formate, and the (003) facet possesses strong CO₂ adsorption capability and a high driving force for hydrogenation, making it particularly favorable for the formation of the *COOH intermediate. This work proposes a precise facet engineering strategy, offering a new approach to address the key challenges of catalytic selectivity and charge separation efficiency in this system.