An energy-saving pH-asymmetric electrolyzer for simultaneous methane conversion and hydrogen production

A subsidiary role of electrochemical neutralization energy (ENE) stored in waste acid/base presents a sustainable and economically viable solution for the production of value-added chemicals and saving energy. Here we demonstrate a pH-asymmetric electrolyzer with a bipolar membrane to realize sustainable and efficient electrocatalytic methane oxidation coupling with hydrogen production at a low energy cost. This approach affords a C1/C2 molecule production rate of up to 2.6 mmol g_NiO^-1 h^-1 with simultaneous H₂ production at a potential as low as 1.4 V. Furthermore, the electrocatalyst achieves sustained catalysis at 1 mA for over 24 h with lower operation voltage by 700 mV under auxiliary ENE supply, which means the cell electricity manner would enable an energy elimination of 36.9% energy saving comparing with state-of-the-art electrolyzers. In situ Raman spectroscopy and density functional theory calculation reveal the catalytic mechanism of the important role of Ni^III-O^∙-Ni^III-O^- for the electrochemical methane oxidation (EOM). Meanwhile, the pH-asymmetric integrated cell with simulated and complex waste acid-base solutions showcases a lower voltage of 1.62 V at 1 mA applied current with the same catalysts. Additionally, the device demonstrates negligible degradation at 10 mA cm^-2, suggesting high overall durability for EOM. Techno-economic evaluation is also conducted to present the energy-saving and profit advantages with less oxygen evolution reaction (OER) competition. This work opens a pathway for prospective applications for the production of commodity chemicals simultaneously in one electrolyzer, which can even turn waste acid and base into resources.