Carbon-based transition metal (TM) single-atom catalysts (SACs) have shown a great potential toward electrochemical water splitting and H2 production. Given that two-dimensional (2D) materials are widely exploited for sustainable energy...

MXenes have been widely used as substrates of hybrid electrocatalysts for water splitting due to their stability and metallic properties. However, tuning MXenes towards superb hydrogen/oxygen evolution reaction (HER/OER) activity has remained elusive. Using first‐principles calculations along with machine learning (ML) based descriptors, it is shown that late transition metal doping is able to significantly promote HER/OER activities. Both single‐atom adsorption onto a stable hollow site above the outer oxygen layer single‐atom catalyst 1 (SAC1), and single‐atom replacement at a sub‐surface metal layer (SAC2) are considered. An adsorbate evolving mechanism (AEM) is preferred for SAC1, while the increased M‐O bond covalency for SAC2 makes lattice oxygen mechanism (LOM) favored. It is found that a single Ni or Co atom embedded into MXenes provides a suitable number of electrons for optimal AEM and raises the O 2p band towards activated LOM. The stability and superb bifunctional catalytic capability of MXene combinations (Ni‐doped Sc3N2O2 and Ni‐doped Nb3C2O2) towards both HER and OER are demonstrated. The electronic and geometric descriptors used in the ML analysis work universally for classification of high‐performing HER/OER catalysts. This work provides a rational strategy for promoting bifunctional electrocatalytic activities based on low‐cost MXenes metals.

To tune single-atom catalysts (SACs) for effective nitrogen reduction reaction (NRR), we investigate various transition metals implanted on boron-arsenide (BAs), boron-phosphide (BP), and boron-antimony (BSb) using density functional theory (DFT). Interestingly, W-BAs shows high catalytic activity and excellent selectivity with an insignificant barrier of only 0.05 eV along the distal pathway and a surmountable kinetic barrier of 0.34 eV. The W-BSb and Mo-BSb exhibit high performances with limiting potentials of −0.19 and −0.34 V. The Bader-charge descriptor reveals that the charge transfers from substrate to *NNH in the first protonation step and from *NH3 to substrate in the last protonation step, circumventing a big hurdle in NRR by achieving negative free energy change of *NH2 to *NH3. Furthermore, machine learning (ML) descriptors are introduced to reduce computational cost. Our rational design meets the three critical prerequisites of chemisorbing N2 molecules, stabilizing *NNH, and destabilizing *NH2 adsorbates for high-efficiency NRR.

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Designing highly efficient bifunctional and multifunctional catalysts for hydrogen/oxygen evolution reaction (HER/OER) and oxygen reduction reaction (ORR) has attracted acute attention, toward the development of clean and renewable energy technologies....