Single-Step Fabrication of BiOI Nanoplates as Gas Diffusion Electrodes for CO 2 Electroreduction to Formate: Effects of Spray Pyrolysis Temperature on Activity and Flooding Propensity.

Bismuth-based electrocatalysts for carbon dioxide (CO 2 ) reduction are notable for their high formate selectivity, scalability, affordability, and low toxicity. Here, we introduced a facile spray pyrolysis method to fabricate catalyst-coated gas diffusion electrodes (GDE) in one step. Our study revealed that deposition temperatures significantly affected the morphology, crystal orientation, and impurity of bismuth oxyiodide (BiOI) nanoplates. Specifically, BiOI prepared at 250 °C (BiOI-250) exhibited exceptional Faradaic efficiency (>90%) for formate production at a high current range (100-300 mA cm -2 ) and demonstrated outstanding stability (>30 h). In situ Raman spectroscopy indicated that BiOI-250's superior performance stemmed from its resilience to microscopic flooding, a failure mechanism observed in low-temperature BiOI. X-ray absorption spectroscopy (XAS) showed that BiOI-250 predominantly consisted of the active Bi 2 O 2 CO 3 phase, while low-temperature BiOI contained a mixture of Bi 2 O 2 CO 3 and the less active Bi metal, formed via the reduction of the Bi 2 O 3 impurity. This impurity led to increased catalyst resistivity, uneven potential distribution, and restructuring, contributing to flooding. Our study underscores the crucial role of catalyst structures in determining electrode performance and flooding propensity, offering key insights for optimizing bismuth-based electrocatalysts for CO 2 reduction.