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MXene quantum dots (MQDs) offer wide applications owing to the abundant surface chemistry, tunable energy‐level structure, and unique properties. However, the application of MQDs in electrochemical energy conversion, including hydrogen evolution reaction (HER), remains to be realized, as it remains a challenge to precisely control the types of surface groups and tune the structure of energy levels in MQDs, owing to the high surface energy–induced strong agglomeration in post‐processing. Consequently, the determination of the exact catalytically active sites and processes involved in such an electrocatalysis is challenging because of the complexity of the synthetic process and reaction conditions. Herein, we demonstrated the spontaneous evolution of the surface groups of the Ti2CTx MQDs (x: the content of O atom), i.e., replacement of the ‐Cl functional groups by O‐terminated ones during the cathode reaction. This process resulted in a low Gibbs free energy (0.26 eV) in HER. Our steady Ti2COx/Cu2O/Cu foam systems exhibited a low overpotential of 175 mV at 10 mA cm−2 in 1 M aq. KOH, and excellent operational stability over 165 h at a constant current density of −10 mA cm−2. [ABSTRACT FROM AUTHOR]

Efficient electrocatalytic reactions require a coordinated active center that may provide a properly reaction intermediates adsorption in water splitting. Herein, a Ni active center coordination reconstruction method achieved by multidimensional modulation of phase transition, iodine coordination, and vacancy defects is designed and implemented. This coordination reconstruction results in the successful synthesis of Ni5P4−xIx/Ni2P nanocorals that show outstanding bifunctional catalytic activity due to deep optimization of the adsorption energy. The overpotentials of hydrogen evolution reaction and oxygen evolution reaction at 10 mA cm−2 are 46 and 163 mV, respectively. Only 1.46 V is required to drive alkaline overall water splitting. Novel coordination environment is investigated by electron paramagnetic resonance spectroscopy and extended X‐ray absorption fine structure spectroscopy. A 4D integrated material design strategy of "thermodynamic stability‐electronic properties‐charge transfer‐adsorption energy" for water‐splitting catalysts is proposed. This coordination reconstruction concept and material design method provide new perspectives for the research of novel catalysts. [ABSTRACT FROM AUTHOR]

The grand challenge in the development of atomically dispersed metallic catalysts is their low metal-atom loading density, uncontrollable localization and ambiguous interactions with supports, posing difficulty in maximizing their catalytic performance. Here, we achieve an interface catalyst consisting of atomic cobalt array covalently bound to distorted 1T MoS2 nanosheets (SA Co-D 1T MoS2). The phase of MoS2 transforming from 2H to D-1T, induced by strain from lattice mismatch and formation of Co-S covalent bond between Co and MoS2 during the assembly, is found to be essential to form the highly active single-atom array catalyst. SA Co-D 1T MoS2 achieves Pt-like activity toward HER and high long-term stability. Active-site blocking experiment together with density functional theory (DFT) calculations reveal that the superior catalytic behaviour is associated with an ensemble effect via the synergy of Co adatom and S of the D-1T MoS2 support by tuning hydrogen binding mode at the interface. While single-atom catalysis offers an efficient materials usage, the ambiguous interactions with supports poses a difficulty in understanding catalytic performances. Here, authors show an ensemble effect via synergy of Co adatoms and the S of MoS2 supports to boost hydrogen evolution activities. [ABSTRACT FROM AUTHOR]

The development of low-price and highly efficient catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has always been challenging with regard to water splitting. Pyrrhotite Fe 7 S 8 has become a research hotspot due to its abundant reserves, high electrical conductivity and excellent catalytic activity. In general, introducing metal heteroatoms into transition metal sulfides (TMSs) can effectively enhance the activity and stability of TMSs. Herein, Co-doped pyrrhotite Fe 7 S 8 nanosheets were obtained by a straightforward two-step method consisting of hydrothermal treatment followed by subsequent heat treatment. Results from XPS analysis and contact angle measurements showed that doping optimized the chemical environment around iron atoms and enhanced the adsorption of water molecules on the surface of Fe 7 S 8 , thereby greatly improving the electrocatalytic efficiency of water electrolysis. Compared with other counterparts, Co 0 · 95 Fe 6 · 05 S 8 exhibited superior OER activity with an overpotential of 311 mV at a current density of 10 mA cm−2, and higher performance towards HER with an overpotential of 284 mV at 10 mA cm−2 in alkaline solution. In sum, Co 0 · 95 Fe 6 · 05 S 8 is promising as a bifunctional catalyst for water splitting under alkaline conditions. [ABSTRACT FROM AUTHOR]

Single-atom catalysts have attracted extensive attention due to their unique performances and high atom utilization. However, is single atom always the best? Here we found a reverse case that nickel metaphosphate (NPO) supported nanoparticles (Ru n) is much better than single atoms (Ru s) for all pH hydrogen evolution. The mass activity of Ru n -NPO is 3.8 times higher than that of Ru s -NPO, and 21.4 times higher than that of Pt/C in alkaline media. The results show that Ru nanoparticle possess lower valence state than single atom, providing optimized Ru-H bond strength and suitable hydrogen adsorption free energy. As a novel support, NPO is also essential for firmly anchoring Ru and transporting electrons for optimizing the d -band center, and eventually accelerating the H 2 O dissociation in rate-limiting Volmer step. This work gives Ru-NPO promising potential for practical hydrogen production, and sheds light on the exploration of supported metal catalysts in energy conversion-related fields. [Display omitted] • Nickel metaphosphate (NPO) supported Ru catalyst is developed for all pH HER. • Ru nanoparticles exhibit better HER activity than Ru single atoms. • NPO optimizes the thermodynamic parameter of Ru through metal-support interactions. • The sluggish kinetics of Ru in Volmer step have been speed up. [ABSTRACT FROM AUTHOR]

Development of efficient electrocatalysts requires construction of catalytic surfaces with moderate H adsorption energy. Here, we address this challenge by Br-induced formation of P-poor defective nickel phosphide and show that the H adsorption energy can be optimized by regulating the vacancy concentration. We show that when such defective Ni 12 P 5−x Br x nanoparticles are distributed on the surface of Ni 2 P nanosheets (Ni 12 P 5−x Br x /Ni 2 P NS), excellent catalytic activity for water splitting is obtained in alkaline media. Density functional theory computations revealed that Br doping induce the formation of a P-poor nickel phosphide with vacancies, leading to an optimal H adsorption strength with a volcano-type relationship. This is the best reported for a non-precious metal phosphide at present: the overpotential for HER is 18 mV at 10 mA cm−2 and 155 mV for OER. This leads to an exceptionally low cell voltage requirement of only 1.44 V to drive overall water splitting in an alkaline electrolyzer. [Display omitted] • Br-induced nickel phosphide formation energy change achieves P-poor defective phase configuration. • Multi-level regulation of vacancy content, morphology and catalytic performance by temperature is achieved. • DFT calculations show that Ni 12 P 5−x Br x shows a volcano-type relationship related to vacancy content. [ABSTRACT FROM AUTHOR]

[Display omitted] • Intramolecular heterostructured carbon nitride is successfully synthesized. • The as-prepared sample exhibits superior photocatalytic hydrogen production. • Rapid separation and transfer of photogenerated carriers in as-prepared sample. • The addition of salt mixture regulates the localized electronic structure. Efficient separation and transfer of photogenerated carriers is vital for efficient photocatalytic hydrogen evolution. We report development of a new type of intramolecular heterostructure graphitic carbon nitride with heptazine-triazine (CN-HT) by use of a one-step thermal polymerization method. This intramolecular heterostructure changes the electronic structure to promote charge transfer and enhances the adsorption of H*. The as-prepared CN-HT exhibits superior photocatalytic hydrogen evolution of 88.29 μmol/h, which is 14.2 times that of pristine CN. The apparent quantum yield is 10.1% at 400 nm and 9.6% at 450 nm. The efficient separation and transfer of photogenerated carriers as well as the expanded visible light absorption in this intramolecular CN heterostructure contribute to the efficient utilization of photogenerated carriers, thus enhancing the photocatalytic hydrogen evolution. [ABSTRACT FROM AUTHOR]

Asymmetric Embedding Benzene Ring in graphite carbon nitride changes local charge distribution and electron transfer kinetics, and promote the photocatalytic water splitting to produce hydrogen at a higher rate. • The A-GCN is successfully prepared using dicyandiamide and terephthalonitrile. • Embedding benzene regulate the localized electronic structure. • Theoretical results predicts the localized asymmetry promotes the charge transfer. • For hydrogen production, the A-GCN-1.0 displays 10.8 times as good as pristine GCN. Preventing the high carrier recombination rate of graphitized C 3 N 4 (GCN) is an urgent problem to be solved for its application as a photocatalyst for hydrogen production. Here, we first rationally embed the benzene ring in GCN to modify the local symmetry without changing its long-order structure. Theoretical calculation predicts that this design can change the electronic structure and promote the effective charge transfer in GCN. The benzene ring embedded GCN is successfully prepared by copolymerization using dicyandiamide and terephthalonitrile as precursors. Photoluminescence (PL) and time-resolved transient PL (TRPL) spectra confirm that the electron transfer efficiency of the benzene ring embed GCN is greatly improved. This nanomaterial displays 10.8 times higher photocatalytic hydrogen production rate than that of pristine GCN with the apparent quantum yield of 11.3% at 400 nm and 9% at 420 nm. This work provides a novel strategy for designing high-efficiency two-dimensional (2D) photocatalytic materials for water splitting. [ABSTRACT FROM AUTHOR]