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Although single-atomically dispersed metal-Nx on carbon support (M-NC) has great potential in heterogeneous catalysis, the scalable synthesis of such single-atom catalysts (SACs) with high-loading metal-Nx is greatly challenging since the loading and single-atomic dispersion have to be balanced at high temperature for forming metal-Nx. Herein, we develop a general cascade anchoring strategy for the mass production of a series of M-NC SACs with a metal loading up to 12.1 wt%. Systematic investigation reveals that the chelation of metal ions, physical isolation of chelate complex upon high loading, and the binding with N-species at elevated temperature are essential to achieving high-loading M-NC SACs. As a demonstration, high-loading Fe-NC SAC shows superior electrocatalytic performance for O2 reduction and Ni-NC SAC exhibits high electrocatalytic activity for CO2 reduction. The strategy paves a universal way to produce stable M-NC SAC with high-density metal-Nx sites for diverse high-performance applications.

Maximizing the number of exposed active sites or regulating the coordination environment of catalysts is important for advanced oxidation processes to produce highly reactive radicals and destroy organic contaminants. Single-atom catalysts (SACs) have great potential as Fenton-like catalysts owing to a high utilization rate of atoms and their unique features bridging the gap between homogeneous and heterogeneous catalysis. Here, single-atom Ni dispersed on N-doped nanoporous carbon (Ni–NC) with a relatively high Ni loading of 9.3 wt% was prepared by a cascade anchoring strategy. Isolated Ni–N4 sites are fully exposed in Ni–NC, which display excellent catalytic activity by activating H2O2 and generating sufficient OH in Fenton-like catalytic oxidation of organic contaminants. Taking the degradation of methylene blue for an example, the degradation rate constant of Ni–NC is up to 0.767 min−1, higher than that of Ni3N/C with an Ni–N structure in interstitial sites of Ni6N2 octahedra (0.226 min−1) and NiO/C with an Ni–O structure (0.016 min−1). Combined with density functional theory (DFT) calculations, the high-density Ni–N4 moiety obtained from high single-atom Ni loading enhances charge transfer at the reaction interface and reduces the free energy barrier for H2O2 activation, thereby enabling a remarkable rapid degradation of contaminants. Moreover, the degradation reactor designed with Ni–NC realizes approximately 100% MB removal during 6 h continuous operation. This work highlights the effect of structure and loading for metal centers on catalytic oxidation reactions. [ABSTRACT FROM AUTHOR]

Developing non‐platinum group metal catalysts for the sluggish hydrogen oxidation reaction (HOR) is critical for alkaline fuel cells. To date, Ni‐based materials are the most promising candidates but still suffer from insufficient performance. Herein, we report an unconventional hcp/fcc Ni (u‐hcp/fcc Ni) heteronanocrystal with multiple epitaxial hcp/fcc heterointerfaces and coherent twin boundaries, generating rugged surfaces with plenty of asymmetric convex sites. Systematic analyses discover that such convex sites enable the adsorption of *H in unusual bridge positions with weakened binding energy, circumventing the over‐strong *H adsorption on traditional hollow positions, and simultaneously stabilizing interfacial *H2O. It thus synergistically optimizes the HOR thermodynamic process as well as reduces the kinetic barrier of the rate‐determining Volmer step. Consequently, the developed u‐hcp/fcc Ni exhibits the top‐rank alkaline HOR activity with a mass activity of 40.6 mA mgNi−1 (6.3 times higher than fcc Ni control) together with superior stability and high CO‐tolerance. These results provide a paradigm for designing high‐performance catalysts by shifting the adsorption state of intermediates through configuring surface sites. [ABSTRACT FROM AUTHOR]

Fe─N─C materials with Fe─N4 sites are considered as most promising non‐precious metal‐based electrocatalysts for low‐cost proton‐exchange‐membrane fuel cells (PEMFCs). Breaking the trade‐off between activity and stability has been a long‐standing challenge in the field of acidic oxygen reduction reaction (ORR). Herein, a "top‐down" thermally‐driven strategy is developed to achieve highly active pyrrolic N‐coordinated Fe sites in a high spin state with Fe atomic cluster (Fen@Fe─Npyrr─C) and discover that the neighboring Fen cluster can synergistically stabilize such vulnerable Fe─N4 sites by inhibiting their protonation. Consequently, the Fen@Fe─Npyrr─C catalysts exhibit much enhanced ORR activity and stability, endowing PEMFCs with a high power density of 804.6 mW cm−2 (testing conditions: 80 °C, 100% RH, 2.0 bar) and over 100 h durability (at 0.5 V). These findings open up opportunities for the exploration of durable Fe─N─C ORR electrocatalysts for non‐precious metal‐based PEMFCs and other applications. [ABSTRACT FROM AUTHOR]