In situ/Operando characterization techniques are powerful to provide fundamental information about molecular structure-activity/selectivity relationships for various catalytic systems under controlled condition. However, the lack of model catalyst, as the major obstacle for deeper understanding on the nature of active sites and reaction mechanisms, hinders the further advancements in catalysis. Fortunately, the rapid development of single-atom catalysts (SACs) offers us new opportunities for capturing the reaction intermediates, identifying the active sites, and even monitoring the dynamic behaviors of both the geometric structure and electronic environment of the catalytic sites at atomic scale. In this review, the recent advances on the in situ/operando characterization techniques including X-ray absorption spectroscopy, scanning tunneling microscopy, Fourier-transform infrared spectroscopy, and etc. for the characterization of SACs are thoroughly summarized. The results from these in situ/operando measurements reveal the crucial role of SACs as model systems for sharpening our understanding on the nature of catalytic sites. Furthermore, the challenges and outlooks in developing in situ/operando techniques for single atom catalysis are discussed.

The key step for rational catalyst design in heterogeneous electrocatalysis is to reveal the distinctive energy profile of redox reactions of a catalyst that give rise to specific activity. However, it is challenging to experimentally obtain the energetics of oxygen redox in oxygen electrocatalysis because of the liquid reaction environment. Here we develop a kinetic model that constructs a quantitative relation between the energy profile of oxygen redox and electrochemical kinetic fingerprints. The detailed study here demonstrates that the kinetic fingerprints observed from experiments can be well described by different energetics of oxygen redox. On the basis of the model, a feasible methodology is demonstrated to derive binding energies of the oxygen intermediates from electrochemical data. The surface property of different catalysts derived from our model well rationalizes the experimental trends and predicts potential directions for catalyst design.

The oxygen evolution reaction (OER) is a key process involved in energy and environment‐related technologies. An ideal OER electrocatalyst should show high exposure of active sites and optimal adsorption energies of oxygenated species. However, earth‐abundant transition‐metal‐based OER electrocatalysts still operate with sluggish OER kinetics. Here, a cation‐exchange route is reported to fabricate cobalt‐vanadium‐iron (oxy)hydroxide (CoV‐Fe0.28) nanosheets with tunable binding energies for the oxygenated intermediates. The formation of an amorphous/crystalline heterostructure in the CoV‐Fe0.28 catalyst boosts the exposure of active sites compared to their crystalline and amorphous counterparts. Furthermore, the synergetic interaction of Co, V, and Fe cations in the CoV‐Fe0.28 catalyst subtly regulates the local coordination environment and electronic structure, resulting in the optimal thermodynamic barrier for this elementary reaction step. As a result, the CoV‐Fe0.28 catalyst exhibits superior electrocatalytic activity toward the OER. A low overpotential of 215 mV is required to afford a current density of 10 mA cm−2 with a small Tafel slope of 39.1 mV dec−1, which outperforms commercial RuO2 (321 mV and 86.2 mV dec−1, respectively).

Driven by the persisting poor understanding of the sluggish kinetics of the hydrogen evolution reaction (HER) on Pt in alkaline media, a direct correlation of the interfacial water structure and activity is still yet to be established. Herein, using Pt and Pt–Ni nanoparticles we first demonstrate a strong dependence of the proton donor structure on the HER activity and pH. The structure of the first layer changes from the proton acceptors to the donors with increasing pH. In the base, the reactivity of the interfacial water varied its structure, and the activation energies of water dissociation increased in the sequence: the dangling O−H bonds < the trihedrally coordinated water < the tetrahedrally coordinated water. Moreover, optimizing the adsorption of H and OH intermediates can re‐orientate the interfacial water molecules with their H atoms pointing towards the electrode surface, thereby enhancing the kinetics of HER. Our results clarified the dynamic role of the water structure at the electrode–electrolyte interface during HER and the design of highly efficient HER catalysts.

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