Saeed Khezar H, Garcia Osorio Dora-Alicia, Li Chao, Banerji Liam, Gardner Adrian M, Cowan Alexander J
Department of Chemistry, Stephenson Institute for Renewable Energy, University of Liverpool Liverpool UK
Early Career Laser Laboratory, University of Liverpool Liverpool UK.
Chem Sci. 2023 Feb 23;14(12):3182-3189. doi: 10.1039/d2sc05628c. eCollection 2023 Mar 22.
To understand the mechanisms of water oxidation on materials such as hematite it is important that accurate measurements and models of the interfacial fields at the semiconductor liquid junction are developed. Here we demonstrate how electric field induced second harmonic generation (EFISHG) spectroscopy can be used to monitor the electric field across the space-charge and Helmholtz layers in a hematite electrode during water oxidation. We are able to identify the occurrence of Fermi level pinning at specific applied potentials which lead to a change in the Helmholtz potential. Through combined electrochemical and optical measurements we correlate these to the presence of surface trap states and the accumulation of holes (h) during electrocatalysis. Despite the change in Helmholtz potential as h accumulate we find that a population model can be used to fit the electrocatalytic water oxidation kinetics with a transition between a first and third order regime with respect to hole concentration. Within these two regimes there are no changes in the rate constants for water oxidation, indicating that the rate determining step under these conditions does not involve electron/ion transfer, in-line with it being O-O bond formation.
为了理解诸如赤铁矿等材料上的水氧化机制，开发半导体 - 液体结处界面场的精确测量方法和模型非常重要。在此，我们展示了电场诱导二次谐波产生（EFISHG）光谱如何用于监测水氧化过程中赤铁矿电极上空间电荷层和亥姆霍兹层的电场。我们能够识别在特定施加电位下费米能级钉扎的发生，这会导致亥姆霍兹电位发生变化。通过结合电化学和光学测量，我们将这些与表面陷阱态的存在以及电催化过程中空穴（h）的积累相关联。尽管随着h的积累亥姆霍兹电位发生了变化，但我们发现可以使用一个种群模型来拟合电催化水氧化动力学，该模型在空穴浓度方面呈现一阶和三阶机制之间的转变。在这两种机制内，水氧化的速率常数没有变化，这表明在这些条件下速率决定步骤不涉及电子/离子转移，这与它是O - O键形成一致。
