Disentangling the Role of Surface Chemical Interactions on Interfacial Charge Transport at BiVO₄ Photoanodes

Abstract

Chemical transformations that occur on photoactive materials, such as photoelectrochemical water splitting, are strongly influenced by the surface properties as well as by the surrounding environment. Herein, we elucidate the effects of oxygen and water surface adsorption on band alignment, interfacial charge transfer, and charge-carrier transport by using complementary Kelvin probe measurements and photoconductive atomic force microscopy on bismuth vanadate. By observing variations in surface potential, we show that adsorbed oxygen acts as an electron-trap state at the surface of bismuth vanadate, whereas adsorbed water results in formation of a dipole layer without inducing interfacial charge transfer. The apparent change of trap state density under dry or humid nitrogen, as well as under oxygen-rich atmosphere, proves that surface adsorbates influence charge-carrier transport properties in the material. The finding that oxygen introduces electronically active states on the surface of bismuth vanadate may have important implications for understanding functional characteristics of water splitting photoanodes, devising strategies to passivate interfacial trap states, and elucidating important couplings between energetics and charge transport in reaction environments.

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“…For instance, the barrier heights between various semiconductors and noble metals (Pt/Ru/Rh) change substantially in the presence of H 2 , 77 and the surface work function and electrical behavior of BiVO 4 are sensitive to the ambient atmosphere (N 2 /O 2 /H 2 O). 78 Thus, the effects of gas adsorption on samples that operate in specific atmospheres need to be elucidated. For example, operando AFM studies of earth-abundant HER, CO 2 R, and OER catalysts should consider the effects of the generation and adsorption of reactants or products on the electrode.…”