Robust CoP-based bifunctional electrodes for 13.2 % efficient PV-driven water electrolysis in alkaline medium

The development of robust and efficient bifunctional non-precious metal-based electrodes for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is pivotal for enhancing the performance of PV-water electrolysis systems. In this study, we report a facile, one-step electrodeposition method for decorating stainless steel felt (SSF) with amorphous cobalt phosphate/phosphide (CoP) nanoparticles, yielding binder-free, conductive, and mechanically robust electrodes for HER and OER reactions in an alkaline environment. Benefiting from the homogeneous nanoparticle deposition, porosity, increased electrochemical surface area (ECSA), and strong interfacial contact between the CoP and SSF substrate, the optimized CoP@SSF electrode demonstrated outstanding OER performance, achieving overpotentials of 234 and 281 mV at current densities of 10 and 100 mA cm⁻², respectively, with a Tafel slope of 51 mV dec⁻¹. For HER, the same electrode exhibited an overpotential of 161 and 245 mV at 10 and 100 mA cm⁻², respectively, with a Tafel slope of 65 mV dec⁻¹, evincing that the developed electrode has bifunctionality and can serve at the OER and HER sides. Durability tests confirmed excellent stability over 130 h under continuous operation at 500 mA cm⁻². Additionally, a laboratory-scale PV-water electrolyzer consisting of a triple junction InGaP/InGaAs/Ge solar cell and CoP@SSF bifunctional electrodes achieved a solar-to‑hydrogen conversion efficiency of 13.2 %. This work introduces a rapid and scalable strategy for developing robust CoP-based bifunctional electrodes, providing a promising route for demonstrating high-performance PV-water electrolysis systems for green hydrogen production from an alkaline medium.