A sodium-ion-conducted asymmetric electrolyzer to lower the operation voltage for direct seawater electrolysis
Hao Shi, Tanyuan Wang, Jianyun Liu, Weiwei Chen, Shenzhou Li, Jiashun Liang, Shuxia Liu, Xuan Liu, Zhao Cai, Chao Wang, Dong Su, Yunhui Huang, Lior Elbaz, Qing Li
Abstract
Abstract Hydrogen produced from neutral seawater electrolysis faces many challenges including high energy consumption, the corrosion/side reactions caused by Cl - , and the blockage of active sites by Ca 2+ /Mg 2+ precipitates. Herein, we design a pH-asymmetric electrolyzer with a Na + exchange membrane for direct seawater electrolysis, which can simultaneously prevent Cl - corrosion and Ca 2+ /Mg 2+ precipitation and harvest the chemical potentials between the different electrolytes to reduce the required voltage. In-situ Raman spectroscopy and density functional theory calculations reveal that water dissociation can be promoted with a catalyst based on atomically dispersed Pt anchored to Ni-Fe-P nanowires with a reduced energy barrier (by 0.26 eV), thus accelerating the hydrogen evolution kinetics in seawater. Consequently, the asymmetric electrolyzer exhibits current densities of 10 mA cm −2 and 100 mA cm −2 at voltages of 1.31 V and 1.46 V, respectively. It can also reach 400 mA cm −2 at a low voltage of 1.66 V at 80 °C, corresponding to the electricity cost of US$1.36 per kg of H 2 ($0.031/kW h for the electricity bill), lower than the United States Department of Energy 2025 target (US$1.4 per kg of H 2 ).