Co-production of hydrogen, oxygen, and electricity via an integrated solar-driven system with decoupled water electrolyzer and Na-Zn ion battery

Combining water electrolysis and rechargeable battery technologies into a single system holds great promise for the co-production of hydrogen (H₂) and electricity. However, the design and development of such systems is still in its infancy. Herein, an integrated hydrogen-oxygen (O₂)-electricity co-production system featuring a bipolar membrane-assisted decoupled electrolyzer and a Na-Zn ion battery was established with sodium nickelhexacyanoferrate (NaNiHCF) and Zn²⁺/Zn as dual redox electrodes. The decoupled electrolyzer enables to produce H₂ and O₂ in different time and space with almost 100% Faradaic efficiency at 100 mA cm⁻². Then, the charged NaNiHCF and Zn electrodes after the electrolysis processes formed a Na-Zn ion battery, which can generate electricity with an average cell voltage of 1.75 V at 10 mA cm⁻². By connecting Si photovoltaics with the modular electrochemical device, a well-matched solar driven system was built to convert the intermittent solar energy into hydrogen and electric energy with a solar to hydrogen-electricity efficiency of 16.7%, demonstrating the flexible storage and conversion of renewables.