Decoupled Green Hydrogen Production Using Platinum Free Catalysts in a Bicarbonate Electrolyte

Abstract

Electrochemical water splitting is crucial for decarbonizing industrial processes and integrating renewable energy. Conventional electrolysers generate H₂ and O₂ simultaneously in neighbouring compartments using critical raw materials (CRM) as catalysts and corrosive electrolytes, posing safety and cost challenges. Decoupled electrolysis addresses this by separating product formation from electrode processes using electrochemically generated redox mediators and highly dispersed catalysts instead of electrodes and heterogeneous two-dimensional interfaces. In this work we demonstrate decoupled electrolysis at near-neutral pH using a bicarbonate buffer and a highly reducing redox mediator, chromium propanediamine tetraacetate. We compared CRM-free electrocatalysts, MoS₂, Mo₂C, Ni, NiₓSy, and NiₓPy against V10Pt (Vulcan carbon with 10% Pt loading), with MoS₂ showing the highest faradaic efficiency. We further analyzed hydrogen evolution reaction (HER) kinetics and thermodynamics using open circuit chronopotentiometry (OCCP) and UV-vis spectroscopy to follow mediator discharge with MoS₂. Finally, we compare the performance of a conventional electrolyser with MoS2 catalysts in bicarbonate with the decoupled approach, and find that the decoupled performance is superior, despite the energy penalty of -0.6 V. This approach offers a safer, CRM-free alternative to conventional water electrolysis and is compatible with renewable energy storage and green electricity integration.