Coupling Ferrocyanide-Assisted PW/PB Redox with Efficient Direct Seawater Electrolysis for Hydrogen Production
Xin Jia, Hongjun Kang, Guangyao Hou, Songtao Lu, Yuan Yao, Qing Wang, Wei Qin, Xiaohong Wu
Abstract
Direct seawater electrolysis is a promising approach for grid-scale hydrogen mass production. However, the low energy efficiency and detrimental anodic chlorine electrochemistry unlock its practical potential. Here, we present an efficient chlorine-free hydrogen production by coupling the rapid electrode reaction of ferrocyanide-assisted Prussian white (PW)/Prussian blue (PB) redox with an onset potential of 0.87 V RHE . The chloride oxidation in our cells is avoided by low cell voltages, enabling high-purity hydrogen production. Operando spectroscopic analysis coupled with theoretical calculations validates that the addition of the [Fe(CN) 6 ] 3–/4– redox mediator in the electrolyte can reduce the PB to PW instantaneously, thus completing the cycle of PW/PB redox and making the system recyclable. The assembled electrolyzer exhibited unprecedented performance for direct seawater electrolysis (pH = 8.5), achieving a current density of 320 mA cm –2 at 1.7 V. Therefore, the electricity consumed per cubic meter of H 2 produced in the electrolyzer is 3.8 kWh at 200 mA cm –2, and 42% lower energy equivalent input relative to commercial redox-free seawater electrolysis. This work offers a cost-competitive and energy-saving strategy for producing high-purity H 2 directly from unlimited seawater.