In situ and operando Raman spectroscopy of semiconducting photoelectrodes and devices for photoelectrochemistry

Abstract

Abstract Future alternative and promising energy sources involve photoelectrochemical (PEC) devices that can convert sunlight and abundant resources such as water and CO2 into chemical fuels and value-added products. However, identifying suitable photoabsorber semiconductor materials that fulfill all the stringent requirements of photoelectrodes in PEC devices remains a significant challenge. A key factor for tailoring and optimizing existing and novel photoabsorbers is understanding the processes occurring at the semiconductor/liquid electrolyte interface under working conditions. This perspective focuses on the application of operando Raman spectroscopy (RS) in synergy with (photo)electrochemical techniques. Despite being a relatively new field of application, when applied to photoelectrochemistry, operando RS offers insights into the evolution of photoelectrode structure (i.e. phase purity and degree of crystallinity) and surface defects under working conditions. The challenges associated with operando RS for (photo)electrochemical applications, including the low quantum efficiency of inelastic scattering and fluorescence, and possible mitigation strategies are discussed. Furthermore, practical aspects such as sample/reactor geometry requirements and the surrounding environment of the photoelectrode sample during operando RS under PEC conditions are reviewed. We demonstrate that operando RS can be used to perform product analysis of solar-driven biomass reforming reactions, showing the approach’s limitations and discussing possible solutions to overcome them. This work concludes with a discussion on the current state of operando RS of semiconducting photoelectrodes and devices for photoelectrochemistry. We show a new methodology for performing operando RS with illumination resembling AM1.5 conditions and with time resolution spanning from tens to hundreds of milliseconds, suitable timescales for real-time monitoring of chemical reactions and degradation mechanisms occurring at the photoelectrode under investigation.