Water Electrolysis in Saturated Phosphate Buffer at Neutral pH

Hydrogen production from renewable energy and ubiquitous water has a potential to achieve sustainability, although current water electrolyzers cannot compete economically with the fossil fuel‐based technology. Here, we evaluate water electrolysis at pH 7 that is milder than acidic and alkaline pH counterparts and may overcome this issue. The physicochemical properties of concentrated buffer electrolytes were assessed at various temperatures and molalities for quantitative determination of losses associated with mass‐transport during the water electrolysis. Subsequently, in saturated K‐phosphate solutions at 80 °C and 100 °C that were found to be optimal to minimize the losses originating from mass‐transport at the neutral pH, the water electrolysis performance over model electrodes of IrOx and Pt as an anode and a cathode, respectively, was reasonably comparable with those of the extreme pH. Remarkably, this concentrated buffer solution also achieved enhanced stability, adding another merit of this electrolyte for water electrolysis. Keeping it neutral: Determination and analysis of physicochemical properties revealed that phosphate solutions at neutral pH achieved smaller mass‐transport losses during water electrolysis at higher molalities and temperatures. Electrocatalytic testing demonstrated water electrolysis in saturated phosphate solutions to be comparable to that in extreme pH counterparts at elevated temperatures.