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Direct estimation of the reaction environment, e.g., local pH at the anode side of a membrane electrode assembly (MEA) of zero gap electrolyzer, is essential to understand possible key factors, which are influencing the sustainable operation of industrial electrolyzers. Herein, we demonstrate a scanning electrochemical microscopy-based strategy to measure the local pH in the close vicinity of an operating MEA. Local proton concentration changes during the oxygen evolution reaction were monitored in the nonzero gap electrolyzer and MEA systems. The measurements constitute a methodology to evaluate the ion transport efficiency of the MEA. The strategy was extended to investigate the effect of an activation process, buffering of the electrolyte, and poisoning effect on the change in proton transport efficiency. This novel strategy enables the estimation of the actual pH of the MEA system during operation and is of great relevance in understanding the process conditions during sustainable fuel production., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

In this paper, the synergistic effect of porosity and gradient of Mo doping in BiVO 4 photoanodes for improving charge separation and solar water oxidation performance is reported. A simple solution-based, three-step fabrication route was adopted using a layer-by-layer assembling technique. A water oxidation photocurrent of ∼1.73 mA cm -2 at 1.23 V vs reversible hydrogen electrode in neutral pH was achieved without using any sacrificial agent or electrocatalyst. The gradient Mo doping was found to enhance charge separation efficiency, which was verified through a shift in the water oxidation onset potential cathodically to ∼200 mV. In addition, these results were further confirmed by a higher open-circuit photovoltage and flat band potential investigations. This was attributed to the surface energetics played by gradient Mo doping that served as the driving force in reducing the onset potential for water oxidation. The coupled effect of enhanced light absorption and charge separation was revealed by monitoring the difference in decoupling the water oxidation efficiencies of porous and planar Mo:BiVO 4 photoanodes. This study demonstrated an improvement in the catalytic and charge separation efficiency of Mo:BiVO 4 photoanodes due to the introduction of porous structured homojunctions in a gradient manner. The simple synthesis approach adopted in the present study can be utilized and scaled up in making efficient photoanodes for competent solar water oxidation cells., Competing Interests: The authors declare no competing financial interest.

Sunlight-responsive anatase N-doped TiO2 thin films undergoing reversible and switchable hydrophobic to superhydrophilic transition were synthesized by ultrasonic spray pyrolysis in a single step. Film thickness, roughness, surface morphology, crystal structure, composition, band gap, and wetting properties were studied using surface profilometry, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, and water contact angle measurements, respectively. Surface X-ray photoelectron spectroscopy before and after sunlight irradiation revealed the major physicochemical process responsible for the hydrophobic → hydrophilic transition as surface hydroxylation and that responsible for hydrophilic → superhydrophilic transition as destruction of surface adsorbed organic species. The kinetic rates of the hydrophobic → superhydrophilic transition under sunlight and superhydrophilic → hydrophobic transition when kept under dark are found to be 0.215 min(-1) and 2.03 × 10(-4) min(-1), respectively.