Rational design of ruthenium (Ru)-based electrocatalyst for efficient hydrogen production

Abstract

Developing new energy resources with high energy density, clean and renewable character is deemed as promising protocol to conquer the depletion crisis of traditional fossil fuels. Water-splitting devices could produce hydrogen with high combustion value, clean product and easily stored character has received enormous attention. Designing the catalyst for the cathode used in the hydrogen evolution reaction (HER) is one of the major concerns of the research community because it has the greatest effect on rapid, high-quantity hydrogen generation. Likewise, the anodic oxygen evolution reaction (OER) proceeds multistep proton-coupled electron transfer is kinetically more sluggish than cathode reaction, which also requires efficient electrocatalyst to accelerate the reaction, reduce the overpotential, and thus enhance the energy conversion efficiency. Ruthenium (Ru) has the appropriate adsorption energies for adsorbed hydrogen (Hads) and oxygen (Oads) as well as a reasonable price, and accordingly is a potential candidate for both efficient HER and OER catalysts. The abundant d-orbital electrons allow Ru to be functionalized with various supports to satisfy reaction kinetics. However, precisely tuning electronic property of Ru moieties with intrinsic chemical and electronic stability remains challenging. First part of this dissertation discussed the nanoparticle supported catalysts with metal-support interaction are capable of modulating electronic structure and improving catalytic performance. We reported that Ru nanoparticles (NPs) can self-accommodate into Fe3O4 and carbon support (Ru-Fe3O4/C) through the electronic metal-support interaction, resulting in robust catalytic activity toward the alkaline hydrogen evolution reaction (HER). The Ru–O bond formed by orbital mixing changes the charge state of the surface Ru site, enabling more electrons to flow to H intermediates (H*) for favorable adsorption. The weak binding strength of the Ru–O bond also reinforces the anti-bonding character of H* with a more favorable recombination of H* species into H2 molecules. Second part of this dissertation investigated the profound impact of intentionally bridged Ru–O bond toward intrinsic chemical and electronic stability of Ru-based catalyst. we reported Ru NPs, formed directly on the surface of an oxidized (Ni(OH)2) nickel foam (NF) electrode, i.e., Ru-Ni(OH)2/NF, via a spontaneous galvanic replacement reaction, which can generate a tunable Ru–O coordination path and permits control of the valence state of Ru NPs. Various characterization suggests that the intrinsic stability of the Ru-Ni(OH)2 catalyst originates from the synergetic modulation of valence state, interfacial electronic interaction, and coordination environment on Ru active sites. The stabilization strategy simultaneously bolsters the OER and HER kinetics of the Ru NPs.