Great enthusiasm in single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) has been aroused by the discovery of M−N X as a promising ORR catalysis center. However, the performance of SACs lags far behind that of stateof-the-art Pt due to the unsatisfactory adsorption−desorption behaviors of the reported catalytic centers. To address this issue, rational manipulation of the active site configuration toward a well-managed energy level and geometric structure is urgently desired, yet still remains a challenge. Herein, we report a novel strategy to accomplish this task through the construction of an Fe−Co dual-atom centered site. A spontaneously absorbed electron-withdrawing OH ligand was proposed to act proactively as an energy level modifier to empower easy intermediate desorption, while the triangular Fe−Co−OH coordination facilitates O−O bond scission. Benefiting from these attributes, the as-constructed FeCoN 5 −OH site enables an ORR onset potential and half-wave potential of up to 1.02 and 0.86 V (vs RHE), respectively, with an intrinsic activity over 20 times higher than the single-atom FeN 4 site. Our finding not only opens up a novel strategy to tailor the electronic structure of an atomic site toward boosted activity but also provides new insights into the fundamental understanding of diatomic sites for ORR electrocatalysis.

A number of important reactions such as the oxygen evolution reaction (OER) are catalyzed by transition metal oxides (TMOs), the surface reactivity of which is rather elusive. Therefore, rationally tailoring adsorption energy of intermediates on TMOs to achieve desirable catalytic performance still remains a great challenge. Here we show the identification of a general and tunable surface structure, coordinatively unsaturated metal cation (MCUS), as a good surface reactivity descriptor for TMOs in OER. Surface reactivity of a given TMO increases monotonically with the density of MCUS, and thus the increase in MCUS improves the catalytic activity for weak-binding TMOs but impairs that for strong-binding ones. The electronic origin of the surface reactivity can be well explained by a new model proposed in this work, wherein the energy of the highest-occupied d-states relative to the Fermi level determines the intermediates' bonding strength by affecting the filling of the antibonding states. Our model for the first time well describes the reactivity trends among TMOs, and would initiate viable design principles for, but not limited to, OER catalysts.

Figure 1. Schematic illustration showing Pt dissolution and redeposition during the HER experiment if Pt is applied as the counter electrode.

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The mechanism and kinetics of the hydrogen oxidation reaction (hor) has been investigated using carbon-supported single particles of Pt electrocatalyst with radii as small as 40 nm. The high mass transport rates on such small particles enable us to investigate the rapid kinetics of the hor in the absence of diffusion limitations. Surface kinetic controlled polarization curves during the electrochemical oxidation of hydrogen molecules in acid solution have been obtained in the entire H UPD region, showing features obviously different from those obtained on normal micrometer electrodes or in RDE experiments. For instance, two current plateaus rather than one are seen during the steady-state polarization of the hor on electrodes made of small particles. Upon decreasing the size of the Pt particles, the two current plateaus show greater separation and become better defined. A theoretical model for the steady-state polarization of the hor has been developed in which UPD H atoms of various states are considered as the reactive intermediates and the Frumkin adsorption mode is assumed for the atomic H on Pt electrodes. It is shown that the first current plateau represents the limiting reaction rate under adsorption or combined adsorption−diffusion control while the second plateau current corresponds to the limiting diffusion-controlled reaction rate. It is pointed out that Tafel plots that have been frequently used for kinetics analysis in the hor are meaningless, especially in the potential region below 0.05V vs RHE. The polarization curves are fitted with a general polarization equation derived according to our model. The fitting shows that the hor on Pt proceeds most likely via the Tafel−Volmer reaction mechanism rather than the Heyrovsky−Volmer mechanism. These results have significant implications on the understanding and modeling of the reactions in solid polymer electrolyte fuel cells.

Although electrocatalysts based on transition metal phosphides (TMPs) with cationic/anionic doping have been widely studied for hydrogen evolution reaction (HER), the origin of performance enhancement still remains elusive mainly due to the random dispersion of dopants. Herein, we report a controllable partial phosphorization strategy to generate CoP species within the Co‐based metal‐organic framework (Co‐MOF). Density functional theory calculations and experimental results reveal that the electron transfer from CoP to Co‐MOF through N‐P/N‐Co bonds could lead to the optimized adsorption energy of H2O (ΔGnormalH2normalO* ) and hydrogen (ΔGH*), which, together with the unique porous structure of Co‐MOF, contributes to the remarkable HER performance with an overpotential of 49 mV at a current density of 10 mA cm−2 in 1 m phosphate buffer solution (PBS, pH 7.0). The excellent catalytic performance exceeds almost all the documented TMP‐based and non‐noble‐metal‐based electrocatalysts. In addition, the CoP/Co‐MOF hybrid also displays Pt‐like performance in 0.5 m H2SO4 and 1 m KOH, with the overpotentials of 27 and 34 mV, respectively, at a current density of 10 mA cm−2.

Searching for non-noble metal based electrocatalysts with high efficiency and durability toward hydrogen evolution reaction (HER) is vitally necessary for the upcoming clean and renewable energy systems. Here we report the synthesis of CoP nanoparticles encapsulated in ultrathin nitrogen-doped porous carbon (CoP@NC) through a metal-organic framework (MOF) route. This hybrid exhibits remarkable electrocatalytic activity toward HER in both acidic and alkaline media, with good stability. The experiment and theoretical calculation reveal that the carbon atoms adjacent to N dopants on the shells of CoP@NC are active sites for hydrogen evolution, and CoP and N dopants synergistically optimize the binding free energy of H* on the active sites, which results in a higher electrocatalytic activity than its counterparts without nitrogen doping and/or CoP-encapsulation.

The synthesis of vertical ReS2 nanowalls on 3D graphene foam (V-ReS2 /3DGF) is demonstrated by a chemical vapor deposition route. The vertical nanowall structure leads to an effective exposure of active sites and enhances the lithium interaction with all of the layers. When serving as the anode material for lithium-ion batteries, the V-ReS2 /3DGF composite demonstrates excellent cycling stability at high-current-density.