Highly Active and Stable Ir, Ru Metal Catalysts on t-ZrO_2-x Supports with Uniform Structure Derived from Metal-Organic Frameworks for Hydrogen Evolution Reaction

Electrocatalysts play a key role in green hydrogen production, essential for establishing sustainable society. Platinum group metals(PGM) are well-known for its high catalytic efficiency and stability for electrochemical hydrogen evolution reactions(HER). However, high cost of PGM hinders practical application of electrocatalysts. Supported metal catalysts are regarded as one of the potential solution by reducing the amount of metal content while maintaining the activity of catalysts. Nitrogen doped carbon and oxides are used as supports for catalyst metals to enhance stability of the catalyst metals in strong acid or basic conditions, even improving the intrinsic activities of catalysts by tuning the electronic structure of metals. Especially oxygen deficient oxides like t-ZrO_2-x are well known for their strong interaction with metals. Due to the abundant oxygen vacancies on the surface of t-ZrO_2-xparticles, metals can be strongly bonded to t-ZrO_2-x particles. Furthermore, various ions and molecules can be absorbed on the surface of t-ZrO_2-x particles in aqueous solution where HER is conducted out. Those surface properties of t-ZrO_2-x particles can promote HER reactions on metal catalysts. In this study, we made the supported metal catalysts with the structure where M(M= Ir, Ru)-ZrO_2-x particles are well dispersed on the porous carbon using metal-organic frameworks(MOF) as a precursor. Uniform structure of M-ZrO_2-x/C was derived from chemically homogeneous nature of MOF. During the pyrolysis process of MOF in inert condition, ZrO₂ nods form t-ZrO_2-x nanoparticles on the conductive carbon matrix. Porous carbon matrix derived from MOF with high surface area facilitates the mass transport in HER. M-ZrO_2-x/C catalyst showed enhanced activity and greatly improved stability compared to commercial catalysts despite of low content of metals. Moreover, we found that surface property of t-ZrO_2-x nanoparticles can promote HER on the metal as a cocatalyst depending on the surrounding conditions.