Ultra-Long Bi Nanowires Coupled With Tapered Si Microwires for Selective Photoelectrochemical CO2-to-Formate Conversion

초록

Photoelectrochemical CO2 reduction offers a promising route to valorize CO2 into value-added chemicals; however, achieving both high efficiency and selectivity remains challenging. The synthesis of ultra-long Bi2O3 nanowires that are electrochemically transformed into metallic Bi nanowires is reported, which exhibit highly efficient and stable CO2 reduction when integrated into electrochemical and photoelectrochemical systems. Rietveld refinement and Halder-Wagner analyses quantify oxygen vacancy formation during the reduction of Bi2O3 to Bi, and theoretical mechanistic studies reveal that these vacancies stabilize the key OCHO intermediate, playing a crucial role in attaining high CO2-to-formate selectivity. The ultra-high aspect ratio of Bi2O3-derived Bi nanowires maximizes the density of electrochemically active sites and facilitates rapid electron transport, collectively contributing to superior CO2 reduction performance. Consequently, the Bi nanowires achieve Faradaic efficiencies above 95% for electrochemical formate production across a wide potential window, with hydrogen evolution effectively suppressed. Motivated by a leaf inspired network, the coupling of Si microwires with Bi nanowires enables efficient charge transfer while preserving light harvesting, functioning as a co-catalyst without blocking incident photons. As a result, the integrated Bi nanowire-tapered Si microwire photoelectrode demonstrates efficient and selective solar-driven CO2-to-formate conversion with outstanding activity and long-term stability under simulated sunlight irradiation.

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