Defect-Rich Low-Crystalline In2S3 Nanosheets for CO2 Electroreduction to Formate

Indium sulfide-based electrocatalysts often suffer from the reduction of In3+ to In0 species in the electrocatalytic CO2 reduction reaction (CO2RR), and this dynamic transformation leads to undesired hydrogen evolution reaction. Promoting the stability of high-valent In3+ species under operating conditions is a challenging but important task for maintaining their excellent electrocatalytic activity. In this work, In2S3 electrocatalysts with controllable crystallinity are synthesized by a hydrothermal reaction at a tunable temperature. The low-crystalline In2S3-1 exhibits more abundant defective and amorphous/crystalline interface structures compared with the high-crystalline ones, thus endowing the low-crystalline In2S3-1 with a higher formate faradaic efficiency (FEformate) of 91.6% at −1.45 V vs RHE in the H-type cell compared with the high-crystalline In2S3-3 (FEformate = 79.3%). This improved electrocatalytic activity can be attributed to its abundant defect structures and amorphous/crystalline interface structures with robustly high-valent In3+ species under the operating conditions. In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy results reveal the *OCHO reaction pathway. Density functional theory (DFT) calculations indicate that defective structures, such as sulfur vacancies, play an important role in lowering the energy barrier for the key intermediate *OCHO formation. This work provides important insight into defect engineering to promote CO2RR.