Novel two-step electrolysis of water suggested for hydrogen production

Recently, a research group led by Prof. CHEN Changlun from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, along with Institute of Energy, Hefei Comprehensive National Science Center, developed advanced cobalt-doped nickel hydroxide bipolar electrodes and non-noble metal catalysts, significantly improving the efficiency and stability of two-step water electrolysis for hydrogen production.

The related results were published in Chemical Engineering Journal and Journal of Colloid and Interface Science.

Traditional alkaline electrolyzers face issues like mismatching with fluctuating renewable energies and hydrogen/oxygen mixing under high pressure, limiting their applications. Two-step water electrolysis addresses these problems by completely separating hydrogen and oxygen production in time and space using a bipolar electrode, eliminating the need for a costly membrane separator. The key is developing high-performance bipolar electrode materials and efficient cell designs. However, commonly used nickel hydroxide electrodes have limitations in electric buffering capacity and charging-discharging stability.

In this study, the team used a one-step electrodeposition method to create cobalt-doped flexible nickel hydroxide bipolar electrodes on carbon cloth. Cobalt doping improved conductivity, electronic cache performance, and prevented parasitic oxygen production during hydrogen production.

They also developed non-noble metal catalysts, including molybdenum-doped nickel cobalt phosphide and plasma-induced iron composite cobalt oxide bifunctional electrodes, which showed high durability and activity. These electrodes enabled hydrogen and oxygen production at different times and places by switching the current direction, resulting in low cell voltages, high decoupling efficiency, and high energy conversion efficiency.

To enhance layered double hydroxide (LDH) electrodes, which suffer from limited capacity and poor conductivity/stability, the team used nonthermal plasma technology to prepare nitrogen-doped nickel-cobalt LDH and nitrogen-doped reduced graphene oxide/nickel-cobalt LDH electrodes, significantly improving capacitance and conductivity.

Two-step water electrolysis is promising for large-scale hydrogen storage and applications like 5G base stations and data centers. "Our performance indicators for two-step water electrolysis for hydrogen production are synchronized with advanced indicators globally, marking an important step towards industrial operation," said Prof. CHEN Changlun.

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