Ru/Ir‐Based Electrocatalysts for Oxygen Evolution Reaction in Acidic Conditions: From Mechanisms, Optimizations to Challenges

Abstract

The generation of green hydrogen by water splitting is identified as a key strategic energy technology, and proton exchange membrane water electrolysis (PEMWE) is one of the desirable technologies for converting renewable energy sources into hydrogen. However, the harsh anode environment of PEMWE and the oxygen evolution reaction (OER) involving four‐electron transfer result in a large overpotential, which limits the overall efficiency of hydrogen production, and thus efficient electrocatalysts are needed to overcome the high overpotential and slow kinetic process. In recent years, noble metal‐based electrocatalysts (e.g., Ru/Ir‐based metal/oxide electrocatalysts) have received much attention due to their unique catalytic properties, and have already become the dominant electrocatalysts for the acidic OER process and are applied in commercial PEMWE devices. However, these noble metal‐based electrocatalysts still face the thorny problem of conflicting performance and cost. In this review, first, noble metal Ru/Ir‐based OER electrocatalysts are briefly classified according to their forms of existence, and the OER catalytic mechanisms are outlined. Then, the focus is on summarizing the improvement strategies of Ru/Ir‐based OER electrocatalysts with respect to their activity and stability over recent years. Finally, the challenges and development prospects of noble metal‐based OER electrocatalysts are discussed.

Constructing Adjustable Heterointerface for Enhancing Acidic Oxygen Evolution Performances of RuO2@CoMnO3 Nanosheets Electrocatalysts

“…Further into this, the d -band center of CMR is −2.55 eV vs. Fermi level (Figure a), which is lower than that of RuO 2 (−1.65 eV). Consequently, the adsorption energy with the reaction intermediates is weakened on the surface of CMR . As depicted in Figure b, the O p -band center of CMR is −3.08 eV lower than that of RuO 2 (−2.70 eV), explaining the lattice oxygen is limited in the acidic OER process .…”

Advancements in water splitting for sustainable energy generation: A review

“…Nano-structuring techniques, such as nanoparticle synthesis, thin-film deposition, or nanowire fabrication, are employed to increase the surface area and expose more active sites. Surface modifications, such as doping, alloying, or surface functionalization, can tailor the catalyst's electronic properties and surface reactivity, leading to improved performance [73][74][75]. Surface functionalization of catalyst is illustrated in Figure 6.…”

Carbon-Encapsulated Ru–Co3O4 Nanosheets as Electrocatalysts for Acidic Water Oxidation

“…So far, Ir-based materials are considered the most effective acidic OER electrocatalysts. However, the scarcity and high cost of Ir-based catalysts have severely restricted their widespread utilization. − In contrast, Ru-based catalysts are more affordable and have high activity compared to Ir-based catalysts, but they suffer from poor durability due to the generation of soluble high-valence Ru species (RuO 4 ) under high oxidation potentials and in acidic environments. − Therefore, it is very important to design effective approaches to improve the stability and activity of Ru-based catalysts in acidic media. − Recently, two major strategies have been employed to address cost and stability issues, such as reducing the Ru content and confining the Ru atoms in an acid-resistant oxide substrate, including WO 3 , Co 3 O 4 , MnO 2 , MoO 3 , Ta 2 O 5 , etc. − Meanwhile, efforts have also been made in other directions, such as alloying Ru with another element, constructing well-defined interfaces through heterostructures, and designing defects (vacancies) rationally. − The electronic interaction between active sites and acid-resistant metal oxide can inhibit the generation of dissolvable high-valence species and regulate the adsorption energy of intermediates on reactive sites, thereby enhancing the stability and activity. For example, Lee and co-workers achieved a high acid-stabile Ir–MoO 3 OER catalyst by creating electron-deficient surfaces .…”