Chromium Oxide-Ruthenium Oxide Solid Solution Anode Implemented in a Solid Phosphate Electrolyzer at 240 °C and 28 Bar Overpressure

This work offers an overview of the synthesis and implementation of various chromium-ruthenium oxide materials for gas-phase solid-acid water electrolysis under hydrothermal conditions (240 °C, 28 bar of Ar and steam overpressure). The oxidic solid solutions show general stability over a broad chromium concentration range in the RuO₂ rutile structure during synthesis. Decomposition of the solid solutions is observed over a potential of around 2.1 V during electrolysis (including the Ohmic contribution of the setup and cell). Electrolysis performed below this decomposition potential shows promising results for replacing pure RuO₂ with a low ruthenium-containing anode. Special attention has been given to Cr_0.6Ru_0.4O₂ for being less expensive because of the lower ruthenium content and showing good stability and comparable performance to RuO₂ during continuous chronopotentiometry operation for 1 h at 75 mA cm⁻² current densities.