The electrocatalytic CO₂RR to produce value‐added chemicals and fuels has been recognized as a promising means to reduce the reliance on fossil resources; it is, however, hindered due to the lack of high‐performance electrocatalysts. The effectiveness of sculpturing metal/metal oxides (MMO) heterostructures to enhance electrocatalytic performance toward CO₂RR has been well documented, nonetheless, the precise synergistic mechanism of MMO remains elusive. Herein, an in operando electrochemically synthesized Cr₂O₃–Ag heterostructure electrocatalyst (Cr₂O₃@Ag) is reported for efficient electrocatalytic reduction of CO₂ to CO. The obtained Cr₂O₃@Ag can readily achieve a superb FE_CO of 99.6% at −0.8 V (vs RHE) with a high J_CO of 19.0 mA cm⁻². These studies also confirm that the operando synthesized Cr₂O₃@Ag possesses high operational stability. Notably, operando Raman spectroscopy studies reveal that the markedly enhanced performance is attributable to the synergistic Cr₂O₃–Ag heterostructure induced stabilization of CO₂^•−/*COOH intermediates. DFT calculations unveil that the metallic‐Ag‐catalyzed CO₂ reduction to CO requires a 1.45 eV energy input to proceed, which is 0.93 eV higher than that of the MMO‐structured Cr₂O₃@Ag. The exemplified approaches in this work would be adoptable for design and development of high‐performance electrocatalysts for other important reactions.

RuO₂ is one of the benchmark electrocatalysts used as the anode material in proton exchange membrane water electrolyser. However, its long‐term stability is compromised due to the participation of lattice oxygen and metal dissolution during oxygen evolution reaction (OER). In this work, weakened covalency of Ru−O bond was tailored by introducing tensile strain to RuO₆ octahedrons in a binary Ru−Sn oxide matrix, prohibiting the participation of lattice oxygen and the dissolution of Ru, thereby significantly improving the long‐term stability. Moreover, the tensile strain also optimized the adsorption energy of intermediates and boosted the OER activity. Remarkably, the RuSnO_x electrocatalyst exhibited excellent OER activity in 0.1 M HClO₄ and required merely 184 mV overpotential at a current density of 10 mA cm⁻². Moreover, it delivered a current density of 10 mA cm⁻² for at least 150 h with negligible potential increase. This work exemplifies an effective strategy for engineering Ru‐based catalysts with extraordinary performance toward water splitting.

The review introduces the mechanisms of heterogeneous hydrogen evolution (HER) and oxygen evolution reactions (OER), summarizesin-situcharacterization techniques and surveys strategies to boost the activities of metal oxide electrocatalysts.