The performance of heterogeneous catalysts in CO₂ methanation depends on various factors that shape their catalytic properties. Understanding these key elements is essential for optimizing catalyst design and enhancing efficiency.

The oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) both are key electrochemical reactions for enabling next generation alternative-power supply technologies. Despite great merits, both of these reactions require robust electrocatalysts for lowering the overpotential and promoting their practical applications in energy conversion and storage devices. Although, noble metal-based catalysts (especially Pt-based catalysts) are at the forefront in boosting the ORR and HER kinetics, high cost, limited availability, and poor stability in harsh redox conditions make them unfit for scalable use. To this end, various strategies including downsizing the catalyst size, reducing the noble metal, and increasing metal utilization have been adopted to appropriately balance the performance and economic issues. This mini-review presents an overview of the current state of the technological advancements in noble metal-based heterogeneous nanocatalysts (NCs) for both ORR and HER applications. More specifically, we focused on establishing the structure–performance correlation.

Single atom catalysts have manifested themselves as a new frontier in heterogeneous catalysis owing to their maximum atom utilization efficiency. However, their tendency to aggregate leads to poor stability, which limits their application. Herein, we overcome this challenge by stabilising a noble metal single atom catalyst through anchoring it on a metal oxide support, where a strong electronic metal–support interaction prevents their aggregation. Specifically, we have synthesized Ru single atoms anchored on the NiCo₂O₄ support by using an ultra-low amount of Ru. XAS and HAADF-STEM analysis confirm the presence of isolated Ru single atoms on the support. These isolated Ru atoms have a high density of unoccupied orbitals, which is favourable for electrocatalytic activity. The synthesized Ru single atom catalyst (Ru-SAC) on NiCo₂O₄ shows superior activity for overall water splitting with a cell potential of 1.57 V, showing excellent stability of 60 h. The synthesized Ru-SAC NiCo₂O₄ is also active in urea electrolysis and exhibits a cell potential of 1.41 V to generate a current density of 10 mA cm⁻². Density functional calculations reveal that supported single Ru atoms optimized the binding energies of the intermediate of both the HER and OER.

Tetrahedral symmetric NiO₂ and Pd respectively facilitate H₂ splitting and CO₂ to CO reduction and thus enable an ultra-high CH₄ production yield performance in the epitaxial interfaces in the bimetallic NiO₂@Pd NPs.

NiO₂ base crystal serves as an electron donor source which injects electrons to Pd nanocrystals by strong electronegativity difference and lattice strain. It creates a high density of active sites on the NC surface and thus improves the HER kinetics.