Transition metal nitrides (TMNs) have great potential for energy-related electrocatalysis because of their inherent electronic properties. However, incorporating nitrogen into a transition metal lattice is thermodynamically unfavorable, and therefore most of the developed TMNs are deficient in nitrogen. Consequently, these TMNs exhibit poor structural stability and unsatisfactory performance for electrocatalytic applications. In this work, we design and synthesize an atomically thin nitrogen-rich nanosheets, Mo5N6, with the help of a Ni-inducing growth method. The as-prepared single-crystal electrocatalyst with abundant metal–nitrogen electroactive sites displays outstanding activity for the hydrogen evolution reaction (HER) in a wide range of electrolytes (pH 0–14). Further, the two-dimensional Mo5N6 nanosheets exhibit high HER activity and stability in natural seawater that are superior to other TMNs and even the Pt benchmark. By combining synchrotron-based spectroscopy and the calculations of electron density of state, we find that the enhanced properties of these nitrogen-rich Mo5N6 nanosheets originates from its Pt-like electronic structure and the high valence state of its Mo atoms.

The development of nonprecious metal electrocatalysts with high activity, low overpotential, and long-term stability for electrocatalytic water splitting has been vigorously investigated. The electrocatalysts include perovskite oxides [7,8] and transition metal oxides/hydroxides [9][10][11] for OER electrocatalysis, and transition metal borides/carbides/nitrides/phosphides/ sulfides/selenides [12][13][14][15][16][17][18][19] for HER electrocatalysis. OER electrocatalysts perform well in basic media, while HER electrocatalysts exhibit excellent activity in acid media. However, the incompatible combination of OER and HER electrocatalysts in the same electrolyte leads to inferior electrocatalytic performance of overall water splitting. Considering sustainable H 2 production, overall seawater splitting is a promising candidate for commercialization toward mass H 2 production. [20] As a result, highly efficient bifunctional electrocatalysts that simultaneously catalyze OER and HER in seawater splitting need to be developed for improving overall water electrolysis efficiency and reducing operation costs. Recent study indicates that the development of alternative bifunctional electrocatalysts for overall seawater electrolysis with high activity and low overpotential is eminently desirable and yet remains challenging. [21] Cobalt selenide, as a typical transition metal dichalcogenide and newly discovered alternative earth-abundant electrocatalyst, has recently drawn broad attention owing to its excellent electrocatalytic activity, high chemical stability, and low cost. [6,22,23] The electrocatalytic activity of cobalt selenide electrocatalysts is mainly ascribed to proper surface active sites, resulting in moderate bonds between Se/Co species in the catalysts and reaction intermediates (*OOH for OER and H* for HER) associated with water electrolysis. The catalyst electrodes are fabricated in hydro/solvothermal route that comprises relatively laborious and sophisticated steps, followed by loading on a current collector by binders. [23][24][25] Alternative synthesis methods are reported as electrochemical deposition [26,27] and direct selenization in open tube. [28,29] However, these methods are unable to manipulate charge state of Co species, resulting in failing to modulate the OER and HER electrocatalytic performance. [30,31] Moreover, the most reported cobalt selenide electrocatalysts for water splitting are CoSe 2 based materials. Only a few case studies on Co 0.85 Se [32] and Co 3 Se 4[33] as electrocatalysts were reported. There is no reported study in the application of cobalt selenide Facile and controllable fabrication of highly active and stable bifunctional electrocatalysts for water electrolysis is important for hydrogen production. 3D cobalt selenide electrodes with CoSe and Co 9 Se 8 phases are synthesized by one-step calcination of Co foil with Se powder in a vacuum-sealed ampoule. The charge state of Co species and the electrocatalytic performance of the prepared catalysts are manipulated by controlling Co...

Common-metal-based single-atom catalysts (SACs) are quite difficult to design due to the complex synthesis processes required. Herein, we report as ingle-atom nickel iodide (SANi-I) electrocatalyst with atomically dispersed nonmetal iodine atoms.T he SANi-I is prepared via as imple calcination step in av acuum-sealed ampoule and subsequent cyclic voltammetry activation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopya nd synchrotron-based X-raya bsorption spectroscopy are applied to confirm the atomic-level dispersion of iodine atoms and detailed structure of SANi-I. Single iodine atoms are found to be isolated by oxygen atoms.The SANi-I is structural stable and shows exceptional electrocatalytic activity for the hydrogen evolution reaction (HER). In situ Raman spectroscopyr eveals that the hydrogen adatom (H ads )i sa dsorbed by as ingle iodine atom, forming the I-H ads intermediate,w hich promotes the HER process.

Electrochemical conversion of CO 2 into ethane is seldom observed because of the generally higher selectivity towards methane, ethylene, and ethanol. Consequently, little experimental evidence for its reaction mechanism exists and thus remains largely unknown. Now, by combining electrochemistry with in situ X-ray absorption fine-structure and in situ Raman techniques, iodide-derived copper (ID-Cu) and oxide-derived copper (OD-Cu) systems were studied to obtain a deeper understanding of the CO 2 to ethane mechanism. With trace iodine species on the surface and positively charged Cu species, production of ethane is significantly more favored on ID-Cu compared to OD-Cu, with higher selectivity and faster kinetics. For the first time, it is experimentally found that the formation of ethane follows the same pathway to ethylene and ethanol, and better stabilization of the late stage ethoxy intermediate can steer the reaction to ethane over ethanol.

2D metal–organic frameworks (MOFs) have been widely investigated for electrocatalysis because of their unique characteristics such as large specific surface area, tunable structures, and enhanced conductivity. However, most of the works are focused on oxygen evolution reaction. There are very limited numbers of reports on MOFs for hydrogen evolution reaction (HER), and generally these reported MOFs suffer from unsatisfactory HER activities. In this contribution, novel 2D Co‐BDC/MoS2 (BDC stands for 1,4‐benzenedicarboxylate, C8H4O4) hybrid nanosheets are synthesized via a facile sonication‐assisted solution strategy. The introduction of Co‐BDC induces a partial phase transfer from semiconducting 2H‐MoS2 to metallic 1T‐MoS2. Compared with 2H‐MoS2, 1T‐MoS2 can activate the inert basal plane to provide more catalytic active sites, which contributes significantly to improving HER activity. The well‐designed Co‐BDC/MoS2 interface is vital for alkaline HER, as Co‐BDC makes it possible to speed up the sluggish water dissociation (rate‐limiting step for alkaline HER), and modified MoS2 is favorable for the subsequent hydrogen generation step. As expected, the resultant 2D Co‐BDC/MoS2 hybrid nanosheets demonstrate remarkable catalytic activity and good stability toward alkaline HER, outperforming those of bare Co‐BDC, MoS2, and almost all the previously reported MOF‐based electrocatalysts.