Active Site Engineering in Transition Metal Based Electrocatalysts for Green Energy Applications

ConspectusHydrogen is widely considered an ideal green energy carrier and a leading candidate to replace nonrenewable fossil fuels and address serious global energy and environmental pollution issues. Scientists worldwide are engaged in developing various technologies related to hydrogen energy exploitation and conversion, such as photocatalytic/electrocatalytic water splitting, fuel cells, and so on. Electrocatalytic water splitting using electric energy can produce clean and pure hydrogen from water on a large scale, which can be further directly converted into electric energy by fuel cells. This environmentally friendly system relies on a series of important reactions, especially the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), which both require high efficiency and durable electrocatalysts. Despite the tremendous efforts of the scientific community, electrocatalysts with satisfactory performance are still lacking. At the heart of electrocatalysts, active sites are key to catalytic performance. Active site engineering, by tuning the nature of the active sites in the electrocatalysts, offers an important opportunity to improve the performance of electrocatalysts. Typically, the strategies for active site engineering involve (1) tailoring the environment around the active sites and (2) engineering the structure of the active sites. These approaches can be used to optimize the electronic properties of the active sites, balance the binding energies between the active sites and the reactants/intermediates/products, and thus accelerate the overall reaction processes.In this Account, we summarize the recent progress made in our laboratory on active site engineering in transition metal based electrocatalysts for green energy applications. We start with metal nanoparticle electrocatalysts, engineering Ru nanoparticles on different supports, to achieve more efficient electrocatalytic HER performance. Next, after we theoretically predicted that the hydrogen adsorption/desorption on iridium (Ir) sites could be balanced by environmental carbon/nitrogen atoms, we anchored Ir nanoparticles on the nitrogenated carbon supports, accelerating the acidic hydrogen evolution catalysis. In subsequent sections, we present how engineering active sites with different structures in metal single atom electrocatalysts achieved enhanced oxygen reduction catalysis. We also demonstrate that active site engineering in metal carbide/phosphide electrocatalysts with defects, surface atomic arrangements and heteroatoms can also improve the catalytic activities of the active sites. This Account highlights the engineering of efficient active sites in transition metal based electrocatalysts using robust strategies, which may offer new opportunities for the rational design and synthesis of efficient electrocatalysts for various energy applications.