Performance Trade-Off in Nickel-Based Hydrogen Evolution Catalysts for Anion Exchange Membrane Water Electrolysis: Effects of the Nickel Oxidation State and Particle Size

The development of green hydrogen through anion exchange membrane water electrolysis (AEMWE) is essential for achieving carbon neutrality. Developing non-precious-metal catalysts for the hydrogen evolution reaction (HER) is crucial for the commercialization of AEMWE. In this study, Ni-CeO2/C catalysts were synthesized via a co-precipitation method and a reduction heat treatment was conducted from 300 to 500 oC to form metallic Ni for the HER. Through this process, CeO2 nanoparticles were uniformly dispersed around Ni metal nanoparticles. Among these catalysts, Ni-CeO2/C 400 exhibited a prominent Ni0 peak according to an XPS analysis and formed smaller nanoparticles compared to Ni-CeO2/C 500, yielding advantageous physicochemical properties for the HER. Subsequently, an electrochemical half-cell LSV analysis demonstrated the lowest HER overpotential of 164 mV at 10 mA cm-2 and a Tafel slope of 89 mV dec-1, suggesting the formation of a trade-off point in the HER performance due to variations in the oxidation state and particle size of the Ni metal. Furthermore, a non-precious-metal-based AEMWE single cell with Ni-CeO2/C 400 as the cathode and Co3O4 as the anode achieved a current density of approximately 700 mA cm-2 at 2.0 Vcell. It also exhibited stable durability at a constant current of 500 mA cm-2 for 100 hours, suggesting the potential for long-term hydrogen production in non-precious-metal-based AEMWE systems.