In Operando Deconvolution of Photovoltaic and Electrocatalytic Performance in ALD TiO2 Protected Water Splitting Photocathodes

<p>Many present-day investigations of water splitting photoelectrodes are based on buried p–n junctions, which usually offer an improved photovoltage and therefore a higher solar-to-hydrogen efficiency in tandem photoelectrochemical cells. In this work, we demonstrate that the dual working electrode (DWE) technique enables the measurement of the surface potential of water splitting buried-junction photocathodes under operation, enabling the deconvolution of the photovoltaic and electrocatalytic performance <i>in operando</i>. Consequently, we can access properties of the buried p–n junction independent of the surface kinetics, and gain information related to the charge transfer through the electrode/electrolyte interface independent of the photovoltaic properties. Moreover, the DWE technique provides a clearer understanding of the photocathode degradation mechanism during stability tests. Two p–n junction-based photocathodes are investigated in this work: a pn<sup>+</sup>-Si/TiO<sub>2</sub> photocathode as model system, and the application of the developed method to the emerging material system Cu<sub>2</sub>O/Ga<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub>. </p>