The electrochemical water splitting to produce hydrogen converts electric energy into clean hydrogen energy, which is a groundbreaking concept of energy optimization. To achieve high efficiency, numerous strategies have been developed to enhance the performance of electrocatalysts. Among these, interface engineering with molecules/ions/groups, serves as a versatile approach for optimizing the performance of electrocatalysts in water splitting. On the basis of numerous achievements in high-performance electrocatalysts engineered through molecules/ions/groups at interface, a comprehensive understanding of these advancements is crucial for guiding future progress. Herein, after providing a concise overview of the background, the interface engineering via molecules/ions/groups for electrocatalytic water splitting is demonstrated from three perspectives. Firstly, the engineering of electronic state of electrocatalysts by molecules/ions/groups at interface to reduce the Gibbs free energy of the corresponding reactions. Secondly, the modification of local microenvironment surrounding electrocatalysts via molecules/ions/groups at interface to enhance the transfer of reactants and products. Thirdly, the protection of electrocatalysts with molecule/ion/group fences improves their durability, including protecting active sites from leaching and defending them against harmful species. The fundamental principles of these three aspects are outlined for each, along with pertinent comments. Finally, several research directions and challenges are proposed.

Alkaline hydrogen evolution reaction (HER) offers a near-zero-emission approach to advance hydrogen energy. However, the activity limited by the multiple reaction steps involving H₂O molecules transfer, absorption, and activation still unqualified the thresholds of economic viability. Herein, we proposed a multisite complementary strategy that incorporates hydrophilic Mo and electrophilic V into Ni-based catalysts to divide the distinct steps on atomically dispersive sites and thus realize sequential regulation of the HER process. The Isotopic labeled in situ Raman spectroscopy describes 4-coordinated hydrogen bonded H₂O to be free H₂O passing the inner Helmholtz plane in the vicinity of the catalysts under the action of hydrophilic Mo sites. Furthermore, potential-dependent electrochemical impedance spectroscopy (EIS) reveals that electrophilic V sites with abundant 3d empty orbitals could activate the lone-pair electrons in the free H₂O molecules to produce more protic hydrogen, and dimerize into H₂ at the Ni sites. By the sequential management of reactive H₂O molecules, NiMoV oxides multisite catalysts surpass Pt/C hydrogen evolution activity (49 mV@10 mA∙cm⁻² over 140 h). Profoundly, this study provides a tangible model to deepen the comprehension of the catalyst–electrolyte interface and create efficient catalysts for diverse reactions.

Nickel-iron layered double hydroxides (NiFe LDHs) represent a promising candidate for oxygen evolution reaction (OER), however, are still confronted with insufficient activity, due to the slow kinetics of electrooxidation of Ni²⁺ cations for the high-valent active sites. Herein, nanopore-rich NiFe LDH (PR-NiFe LDH) nanosheets were proposed for enhancing the OER activity together with stability. In the designed catalyst, the confined nanopores create abundant unsaturated Ni sites at edges, and decrease the migration distance of protons down to the scale of their mean free path, thus promoting the formation of high-valent Ni^3+/4+ active sites. The unique configuration further improves the OER stability by releasing the lattice stress and accelerating the neutralization of the local acidity during the phase transformation. Thus, the optimized PR-NiFe LDH catalysts exhibit an ultralow overpotential of 278 mV at 10 mA∙cm⁻² and a small Tafel slope of 75 mV∙dec⁻¹, which are competitive among the advanced LDHs based catalysts. Moreover, the RP-NiFe LDH catalyst was implemented in anion exchange membrane (AEM) water electrolyzer devices and operated steadily at a high catalytic current of 2 A over 80 h. These results demonstrated that PR-NiFe LDH could be a viable candidate for the practical electrolyzer. This concept also provides valuable insights into the design of other catalysts for OER and beyond.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have proved to possess exceptional catalytic performance for hydrogen evolution and are considered to be an appropriate substitute for commercial Pt-based catalysts. Experimentally, chemical vapor deposition (CVD) is an extremely important technique for acquiring controllable and high-purity TMDs for electrocatalysis and modern electronic devices. Recently, researchers have made significant achievements in synthesizing TMDs used for electrocatalytic hydrogen evolution by CVD ranging from dynamic mechanism exploration to performance optimization. In this review, we present the recent progress based on electrocatalytic hydrogen evolution implemented by CVD-growth TMDs nanosheets and unveil the structural–activity correlation. Firstly, in synthesis, diverse factors covering precursor, substrate, temperature settings, and atmosphere will affect the quality and surface morphology of TMDs. Then, we present the current research status of the CVD-grown 2D TMDs for engineering electrocatalytic hydrogen evolution, including intrinsic performance exploring, morphology engineering, composition adjusting, phase engineering, and vertically-oriented structure constructing. Finally, the future prospects and challenges of CVD in 2D TMDs electrocatalysis are provided.

Sulfide compounds provide a type of promising alternative for oxygen evolution reaction (OER) electrocatalysts due to their diversity, intrinsic activities, low-price and earth-abundance. However, the unsmooth mass transport channel, the collapse of the structure and insufficient intrinsic activities limit their potential for OER performance. In respond, the dense Fe-doped Co₉S₈ nanoparticles encapsulated by S, N co-incorporated carbon nanosheets (Fe-Co₉S₈@SNC) were proposed and synthesized via fast thermal treatment from ultrathin metal-organic frameworks (MOFs) nanosheets. In designed catalysts, the nanosheet configuration connected by nanoparticles retained rich access for permeation of electrolyte and precipitation of O₂ bubbles during OER process. Meanwhile, the outer carbon layer of Co₉S₈ provided additional catalytic activity while acting as armor to keep the structure stability. At the atomic scale, the doped Fe regulated the local charge density and the d-band center for facilitating desorption of oxygen intermediates. Benefiting from this multi-scale regulation strategy, the Fe-Co₉S₈@SNC displays an ultralow overpotential of 273 mV at 10 mA·cm^-2 and small Tafel slope of 55.8 mV·dec^-1, which is even close to the benchmark RuO₂ catalyst. This concept could provide valuable insights into the design of other catalysts for OER and beyond.

Activating basal plane inert sites will endow MoTe₂ with prominent hydrogen evolution reaction (HER) catalytic capability and arouse a new family of HER catalysts. Herein, we fabricated single MoTe₂ sheet electrocatalytic microdevice for in situ revealing the activated basal plane sites by vacancies introducing. Through the extraction of electrical parameters of single MoTe₂ sheet, the in-plane and interlayer conductivities were optimized effectively by Te vacancies due to the defect levels. More deeply, Te vacancies can induce the delocalization of electrons around Mo atoms and shift the d-band center, as a consequence, facilitate the adsorption of H from the catalyst surface for HER catalysis. Benefiting by the coordinated regulation of band structure and local charge density, the overpotential at –10 mA∙cm⁻² was reduced to 0.32 V after Te vacancies compared to 0.41 V for the basal plane sites of same MoTe₂ nanosheet. Meanwhile, the insights gained from single nanosheet electrocatalytic microdevice can be applied to the improved HER of the commercial MoTe₂ power. That the in situ testing of the atomic structure-electrical behavior-electrochemical properties of a single nanosheet before/after vacancies introducing provides reliable insight to structure-activity relationships.