Versatile,Stable, and Scalable Gel-Like Aerophobic Surface System (GLASS) for Hydrogen Production

Facile removal of adsorbed gas bubbles from electrode surfaces is crucial to realize efficient and stable energy conversion devices based on electrochemical gas evolution reactions. Conventional studies on bubble removal have limited applicability and scalability due to their reliance on complex and energy/time-intensive processes. In this study, a simple and versatile method is reported to fabricate large-area superaerophobic electrodes (up to 100 cm²) for diverse gas evolution reactions using the gel-like aerophobic surface system (GLASS). GLASS electrodes are readily and uniformly fabricated by simple spin-coating and cross-linking of polyallylamine on virtually any kinds of electrodes within 5 min under ambient conditions. Intrinsically hydrophilic gel overlayers with interconnected open pores allow the physical separation of bubble adhesion and catalytic active sites, reducing bubble adhesion strength, and promoting the removal of gas bubbles. As a result, GLASS electrodes exhibit greatly enhanced efficiency and stability for diverse gas evolution reactions, such as hydrogen evolution, hydrazine oxidation, and oxygen evolution reactions. This study provides deeper insights into understanding the effect of the hydrophilic microenvironment on gas evolution reactions and designing practical electrochemical devices.     

Lattice and Surface Engineering of Ruthenium Nanostructures for Enhanced Hydrogen Oxidation Catalysis

Ru has recently been considered as a promising alternative of Pt toward hydrogen oxidation reaction (HOR) due to its lower price and similar hydrogen binding energy (HBE) in comparison to Pt. Nevertheless, the catalytic performance of Ru toward HOR is far from the satisfaction of practical application. Herein, it is demonstrated that the modification of Ru multi-layered nanosheet (MLNS) with Ni can significantly promote the HOR performance. In particular, the HOR performance is strongly related to the Ni location on the surface or in the lattice of Ru MLNS. Experimental and theoretical investigations suggest that Ni in the lattice of Ru MLNS (lattice engineering) optimizes the HBE, while Ni species on the surface (surface engineering) decrease the free energy of water formation, as a result of the significantly enhanced HOR performance. The optimal catalyst, where Ni is located both on the surface and in the lattice, displays superior alkaline HOR performance to commercial Pt/C and Ru/C. The present study not only systematically reveals the significance of Ni modification on Ru toward HOR, but also promotes the fundamental researches on catalyst design for fuel cell reactions and beyond.     

Modulating Local Interfacial Bonding Environment of Heterostructures for Energy-Saving Hydrogen Production at High Current Densities

Coupling urea oxidation reaction (UOR) with hydrogen evolution reaction (HER) is an effective energy-saving technique for hydrogen generation. However, exploring efficient bifunctional electrocatalysts under high current density is still challenging. Herein, hierarchical Fe doped cobalt selenide coupled with FeCo layered double hydroxide (Fe-Co_0.85Se/FeCo LDH) array as a self-supported superior bifunctional heterojunction electrode is rationally designed for both UOR and HER. The unique heterostructure facilitates electron transfer and interface interactions through local interfacial Co-Se/O-Fe bonding environment modulation, improving reaction kinetics and intrinsic activity. As a result, the heterostructured electrocatalyst exhibits ultralow potentials of −0.274 and 1.48 V to reach 500 mA cm⁻² for catalyzing the HER and UOR, respectively. Particularly, the full urea electrolysis system driven by Fe-Co_0.85Se/FeCo LDH delivers 300 mA cm⁻² at a relatively low potential of 1.57 V, which is 150 mV lower than the conventional water electrolysis. The combination of in situ characterization and theoretical analysis reveal that the active sites with the adjustable electronic environment are induced by the interfacial bonding of the heterojunction, facilitating the water decomposition of HER and the stabilization of intermediates in UOR. This work inspires the interfacial environment modulation to optimize advanced electrocatalysts for energy-saving H₂ production.     

Modulation of Electron Structure and Dehydrogenation Kinetics of Nickel Phosphide for Hydrazine-Assisted Self-Powered Hydrogen Production in Seawater

The electrocatalytic production of hydrogen from seawater provides a low-cost way to realize energy conversion, but is restricted by high potential for seawater electrolysis and the chlorine oxidation reaction (ClOR) at the anode. Here, the self-growth of Mo-doped Ni₂P nanosheet arrays with rich P vacancies on molybdenum-nickel foam (MNF) (Mo-Ni₂P_v@MNF) is reported as bifunctional catalyst for Cl-free hydrogen production by coupling hydrogen evolution reaction (HER) with hydrazine oxidation reaction (HzOR) in seawater. Impressively, the Mo-Ni₂P_v@MNF electrode as bifunctional catalyst has an excellent activity for overall hydrazine splitting (OHzS) with an ultralow voltage of only 571 mV at 1000 mA cm⁻² and can maintain stability for an ultra-long time of 1000 h at 100 mA cm⁻². Moreover, integration of OHzS into self-assembled hydrazine fuel cells (DHzFC) or solar cells can enable the self-powered H₂ production. The industrial hydrazine sewage as feed for the above eletrolysis system can be degraded to ≈5 ppb rapidly. Density functional thoery calculations demonstrate that the electronic structure modulation induced by P vacancies and Mo doping can not only achieve thermoneutral ΔG_H* for hydrogen evolution reaction but also enhance dehydrogenation kinetics from *N₂H₄ to *NHNH₂ for HzOR, achieving enhanced dehydrogenation kinetics.     

Rational Design of Transition Metal Phosphide-Based Electrocatalysts for Hydrogen Evolution

Developing efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER) is critical to the commercial viability of electrochemical clean energy technologies. Transition metal phosphides (TMPs), with the merits of abundant reserves, unique structure, tunable composition, and high electronic conductivity, are recognized as attractive HER catalytic materials. Nevertheless, the HER electrocatalytic activity of TMPs is still limited by various thorough issues and inherent performance bottlenecks. In this review, these issues are carefully sorted, and the corresponding reasonable explanations and solutions are elucidated on the basis of the HER catalytic activity origins of TMPs. Subsequently, highly targeted multiscale strategies to improve the HER performance of TMPs are comprehensively presented. Additionally, critical scientific issues for constructing high-efficiency TMP-based electrocatalysts are proposed. Finally, the HER reaction process, catalytic mechanism research, TMP-based catalyst construction, and their application expansion are mentioned as challenges and future directions for this research field. Expectedly, this review offers professional and targeted guidelines for the rational design and practical application of TMP-based HER catalysts.     

Bifunctional Co3S4 Nanowires for Robust Sulfion Oxidation and Hydrogen Generation with Low Power Consumption

Sulfion oxidation reaction holds great potential for replacing kinetically sluggish water oxidation to save power consumption and simultaneously purifying environmental sulfion-rich sewage. However, it is still challenged by the insufficient mechanism understanding and questionable stability caused by sulfur passivation. Here, it is demonstrated that bifunctional Co₃S₄ nanowires for assembling hybrid seawater electrolyzer that combines anodic sulfion oxidation and cathodic seawater reduction with an ultra-low power consumption of 1.185 kWh m⁻³ H₂ under 100 mA cm⁻², saving energy consumption over 70% compared to the traditional water splitting system. Unlike water is oxidized into O₂ at high potentials under alkaline water splitting system, experiments combined with in situ characterizations uncover the stepwise oxidation of S²⁻ to short-chain polysulfides and then to value-added product of S₈. Density functional theory calculations prove that Co₃S₄ possesses reduced energy barriers in the rate-determining S₃²⁻ to S₄⁻ oxidation step and S₈ desorption step, promoting conversion of short-chain polysulfides and efficient desorption of S₈. These findings reveal the catalytic mechanism of sulfion oxidation and inspire an economic approach toward the fabrication of bifunctional Co₃S₄ for achieving energy-saving hydrogen production from seawater while rapidly disposing sulfion-rich sewage with boosted activity and stability.     

Triple Interface Optimization of Ru-based Electrocatalyst with Enhanced Activity and Stability for Hydrogen Evolution Reaction

A challenging task is to promote Ru atom economy and simultaneously alleviate Ru dissolution during the hydrogen evolution reaction (HER) process. Herein, Ru nanograins (≈1.7 nm in size) uniformly grown on 1T-MoS₂ lace-decorated Ti₃C₂T_x MXene sheets (Ru@1T-MoS₂-MXene) are successfully synthesized with three types of interfaces (Ru/MoS₂, Ru/MXene, and MoS₂/MXene). It gives high mass activity of 0.79 mA µg_Ru⁻¹ at an overpotential of 100 mV, which is ≈36 times that of Ru NPs. It also has a much smaller Ru dissolution rate (9 ng h⁻¹), accounting for 22% of the rate for Ru NPs. Electrochemical tests, scanning electrochemical microscopy measurements combined with DFT calculations disclose the role of triple interface optimization in improved activity and stability. First, 2D MoS₂ and MXene can well disperse and stabilize Ru grains, giving larger electrochemical active area. Then, Ru/MoS₂ interfaces weakening H^* adsorption energy and Ru/MXene interfaces enhancing electrical conductivity, can efficiently improve the activity. Next, MoS₂/MXene interfaces can protect MXene sheet edges from oxidation and keep 1T-MoS₂ phase stability during the long-term catalytic process. Meanwhile, Ru@1T-MoS₂-MXene also displays superior activity and stability in neutral and alkaline media. This work provides a multiple-interface optimization route to develop high-efficiency and durable pH-universal Ru-based HER electrocatalysts.     

Modification of the Intermediate Binding Energies on Ni/Ni3N Heterostructure for Enhanced Alkaline Hydrogen Oxidation Reaction

Developing highly efficient and stable non-precious metal-based electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is essential for the commercialization of alkaline exchange membrane fuel cells but remains a big challenge. Here, a simple strategy for constructing the Ni/Ni₃N heterostructure electrocatalyst with remarkable catalytic performance toward HOR under alkaline electrolyte is reported. Density functional theory calculations and experimental results reveal that the inter-regulated d-band center of interfacial Ni and Ni₃N derived from electron transfer from Ni to Ni₃N across the interface can lead to the weakened hydrogen binding energy of Ni and strengthened hydroxyl binding energy of Ni₃N, which, together with the decreased formation energy of water species, contributes to the outstanding HOR performance.     

Proximity Electronic Effect of Ni/Co Diatomic Sites for Synergistic Promotion of Electrocatalytic Oxygen Reduction and Hydrogen Evolution

The modulation effect manifests an encouraging potential to enhance the performance of single-atom catalysts; however, the in-depth study about this effect for the isolated diatomic sites (DASs) remains a great challenge. Herein, a proximity electronic effect (PEE) of Ni/Co DASs is proposed that is anchored in N-doped carbon (N-C) substrate (NiCo DASs/N-C) for synergistic promoting electrocatalytic oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Benefiting from the PEE of adjacent Ni anchored by four nitrogen (Ni-N₄) moiety, NiCo DASs/N-C catalyst exhibits superior ORR and HER activity. In situ characterization results suggest Co anchored by four nitrogen (Co-N₄) as main active site for O₂ adsorption-activation process, which promotes the formation of key *OOH and the desorption of *OH intermediate to accelerate the multielectron reaction kinetics. Theoretical calculation reveals the adjacent Ni-N₄ site as a modulator can effectively adjust the electronic localization of proximity Co-N₄ site, promoting the *OH desorption and *H adsorption on Co-N₄ site, thereby boosting ORR and HER process significantly. This study opens a new opportunity for rationally regulating the electronic localization of catalytic active centers by proximity single-atom moiety, as well as provides guidance for designing high-efficiency bifunctional electrocatalysts for promising applications.     

Revisiting the Role of Active Sites for Hydrogen Evolution Reaction through Precise Defect Adjusting

2D transition metal dichalcogenides (TMDs) have presented outstanding potential for efficient hydrogen evolution reaction (HER) to replace traditional noble metal catalysts. Here, to achieve enhanced HER performance, specific areas of the few‐layer 1T'‐MoTe₂ film are precisely controlled with a focused ion beam to create particular active sites. Electrochemical measurements indicate that the HER performance, although inconspicuous in pristine 1T'‐MoTe₂ ultrathin films prepared through the chemical vapor deposition method, can be greatly enhanced after patterning and precisely controlled by the morphologies as well as the amounts of the defects, reaching a small onset potential and a record‐low Tafel slope of 44 mV per decade for few‐layer TMDs. Conductivity tests, visualized copper electrodeposition, and density functional theory calculations also confirm that the enhancement of HER performance comes from the exposed edges by patterning. In this pioneering work, not only is the catalysis mechanism of the edge active sites of 1T'‐MoTe₂ unveiled, but also a universal route to study the properties of 2D materials is demonstrated.