Artificial Heterointerfaces Achieve Delicate Reaction Kinetics towards Hydrogen Evolution and Hydrazine Oxidation Catalysis

CoP Nanoparticle Confined in P, N Co-Doped Porous Carbon Anchored on P-Doped Carbonized Wood Fibers with Tailored Electronic Structure for Efficient Urea Electro-Oxidation

Electronic structure optimization and architecture modulation are widely regarded as rational strategies to enhance the electrocatalysts catalytic performance. Herein, a hybridization of ZIF-67-derived CoP nanoparticles embedded in P, N co-doped carbon matrix (PNC) and anchored on P-doped carbonized wood fibers (PCWF) is constructed using a simple simultaneous phosphorization and carbonization strategy. Benefiting from the optimized surface/interface electronic structures, abundant exposed active sites, and outstanding conductivity, the CoP@PNC/PCWF can drive the urea oxidation reaction (UOR) with greater activity and better stability than most recently reported electrocatalysts, in which a potential as low as 1.32 V (vs reversible hydrogen electrode, RHE) is needed to reach 50 mA cm^-2 and shows excellent durability. Furthermore, for overall urea splitting, using the CoP@PNC/PCWF electrocatalyst as the anode and commercial Pt/C supported on nickel foam as the cathode, an ultralow cell voltage of 1.50 V (vs RHE) is expected to achieve the 50 mA cm^-2 and operate continuously for more than 50 h at 20 mA cm^-2 . The reported strategy may shed light on the use of renewable resources to design and synthesize high-performance non-Ni-based phosphides UOR electrocatalysts for energy-saving H₂ production.

Nanoscale Double-Heterojunctional Electrocatalyst for Hydrogen Evolution

The active sites and charge/mass transfer properties in electrocatalysts play vital roles in kinetics and thermodynamics of electrocatalysis, and impose direct impacts on electrocatalytic performance, which cannot be achieved by a simplex structure. As a prototype, the authors propose a double-heterojunctional nanostructure of NiS2 /Ni3 C@C containing NiS2 /Ni3 C and Ni3 C/C heterojunctions as a general model to optimize the above issues and boost electrocatalytic performance. During the thermal reorganization, the in situ reaction between NiS2 nanoparticles and carbon induces the formation of Ni3 C between them and constructs tightly contacted two kinds of interfaces among the three components. The TEM and XPS reveal the intimately contacted three components and the as-constructed interacted dual interfaces, further confirming the formation of a porous double-heterojunctional nanostructure. Theoretical calculations uncover that the electron density redistribution occurs at Ni3 C/C interface by spontaneous electron transfer from defected carbon to Ni3 C and lower ΔGH* achieves at NiS2 /Ni3 C interface by the concentrated interfacial charge density, which favors the simultaneous realization of high catalytic activity and rapid charge/mass transfer. When applied for hydrogen evolution reaction (HER), the porous double-heterojunctional NiS2 /Ni3 C@C exhibits excellent HER activity and durability among all pH values. Profoundly, this special double-heterojunctional structure can provide a new model for high-performance electrocatalysts and beyond.

Cerium-induced lattice disordering in Co-based nanocatalysts promoting the hydrazine electro-oxidation behavior

In this work, cerium-incorporated Co-based catalysts encapsulated in nitrogen-doped carbon were fabricated for the electrocatalytic hydrazine oxidation reaction (HzOR). The Ce incorporation could lead to the formation of surface oxide nanolayers with a disordered lattice, endowing the catalyst with enriched active sites and enhanced intrinsic activity for promoted HzOR.

Phase-Selective Synthesis of Ruthenium Phosphide in Hybrid Structure Enables Efficient Hybrid Water Electrolysis Under pH-Universal Conditions

Hydrazine-assisted hybrid water electrolysis is an energy-saving approach to produce high-purity hydrogen, whereas the development of pH-universal bifunctional catalysts encounters a grand challenge. Herein, a phase-selective synthesis of ruthenium phosphide compounds hybrid with carbon forming pancake-like particles (denoted as Ru_x P/C-PAN, x = 1 or 2) is presented. The obtained RuP/C-PAN exhibits the highest catalytic activity among the control samples, delivering ultralow cell voltages of 0.03, 0.27, and 0.65 V to drive 10 mA cm^-2 using hybrid water electrolysis corresponding to pH values of 14, 7, and 0, respectively. Theoretical calculation deciphers that the RuP phase displays optimized free energy for hydrogen adsorption and reduced energy barrier for hydrazine dehydrogenation. This work may not only open up a new avenue in exploring universally compatible catalyst to transcend the limitation on the pH value of electrolytes, but also push forward the development of an energy-saving hydrogen generation technique based on emerging hybrid water electrolysis.

Robust Porous WC-Based Self-Supported Ceramic Electrodes for High Current Density Hydrogen Evolution Reaction

Developing an economical, durable, and efficient electrode that performs well at high current densities and is capable of satisfying large-scale electrochemical hydrogen production is highly demanded. A self-supported electrocatalytic "Pt-like" WC porous electrode with open finger-like holes is produced through industrial processes, and a tightly bonded nitrogen-doped WC/W (WC-N/W) heterostructure is formed in situ on the WC grains. The obtained WC-N/W electrode manifests excellent durability and stability under multi-step current density in the range of 30-1000 mA cm-2 for more than 220 h in both acidic and alkaline media. Although WC is three orders of magnitude cheaper than Pt, the produced electrode demonstrates comparable hydrogen evolution reaction performance to the Pt electrode at high current density. Density functional theory calculations attribute its superior performance to the electrode structure and the modulated electronic structure at the WC-N/W interface.

Engineering Interface on a 3D CoxNi1-x(OH)2@MoS2 Hollow Heterostructure for Robust Electrocatalytic Hydrogen Evolution

Clarifying the responsibilities and constructing the synergy of different active phases are of great significance but still an urgent challenge for the heterostructure catalyst to improve the hydrogen evolution reaction (HER) process. Here, three-dimensional (3D) Co_xNi_(1-x)(OH)₂ hollow structure integrating MoS₂ nanosheet catalysts [Co_xNi_(1-x)(OH)₂@MoS₂] were ingeniously designed and prepared. This unique structure has realized the construction of a dual active phase for the optimized stepwise-synergetic hydrogen evolution process over a universal pH range through interface assembly engineering. Meanwhile, the 3D hollow heterostructure with a high surface-to-volume ratio can effectively avoid the agglomeration of MoS₂ and enhance the Co_xNi_(1-x)(OH)₂-MoS₂ heterointerfaces. Thus, superior HER activity and stability were obtained over the universal pH range. Density functional theory calculation reveals that Co_xNi_(1-x)(OH)₂ and MoS₂ phases provide efficient active sites for rate-determining water dissociation and H* adsorption/H₂ generation on Co_xNi_(1-x)(OH)₂-MoS₂ heterointerfaces, respectively, resulting in an optimized energy barrier for HER. This work proposes a constructive strategy to design highly efficient electrocatalysts based on the heterointerface with a defined responsible active phase of electrocatalysts.

Ni3N/Co4N nanosheet heterojunction electrocatalyst for hydrogen evolution reaction in alkaline fresh water/simulated seawater

The Ni3N/Co4N nanosheet heterojunction exhibits higher HER activity in alkaline fresh water and simulated seawater.

Accelerating hydrazine-assisted hydrogen production kinetics with Mn dopant modulated CoS2 nanowire arrays

The designed Mn-modified CoS2 catalyst exhibits outstanding bifunctional electrocatalytic performances toward hydrogen evolution reaction and hydrazine oxidation reaction for high-efficiency energy-saving H2 production by water-assisted electrolysis.

Environmentally benign general synthesis of nonconsecutive carbon-coated RuP2 porous microsheets as efficient bifunctional electrocatalysts under neutral conditions for energy-saving H2 production in hybrid water electrolysis

A nonconsecutive carbon-coated RuP2 porous microsheet (RuP2@InC-MS) with bifunctionality for HzOR and HER is realized. DFT calculations evidence that C is more thermoneutral for HER while Ru boosts the dehydrogenation kinetics during HzOR process.

Three-Phase Heterojunction NiMo-Based Nano-Needle for Water Splitting at Industrial Alkaline Condition

Constructing heterojunction is an effective strategy to develop high-performance non-precious-metal-based catalysts for electrochemical water splitting (WS). Herein, we design and prepare an N-doped-carbon-encapsulated Ni/MoO2 nano-needle with three-phase heterojunction (Ni/MoO2@CN) for accelerating the WS under industrial alkaline condition. Density functional theory calculations reveal that the electrons are redistributed at the three-phase heterojunction interface, which optimizes the adsorption energy of H- and O-containing intermediates to obtain the best ΔGH* for hydrogen evolution reaction (HER) and decrease the ΔG value of rate-determining step for oxygen evolution reaction (OER), thus enhancing the HER/OER catalytic activity. Electrochemical results confirm that Ni/MoO2@CN exhibits good activity for HER (ƞ-10 = 33 mV, ƞ-1000 = 267 mV) and OER (ƞ10 = 250 mV, ƞ1000 = 420 mV). It shows a low potential of 1.86 V at 1000 mA cm-2 for WS in 6.0 M KOH solution at 60 °C and can steadily operate for 330 h. This good HER/OER performance can be attributed to the three-phase heterojunction with high intrinsic activity and the self-supporting nano-needle with more active sites, faster mass diffusion, and bubbles release. This work provides a unique idea for designing high efficiency catalytic materials for WS.

Vanadium-Doping and Interface Engineering for Synergistically Enhanced Electrochemical Overall Water Splitting and Urea Electrolysis

Fabricating effective non-precious metal-based catalysts for hydrogen production via electrochemical water splitting is of considerable importance but remains challenging. Transition metal nitrides possessing metallic character and corrosion resistance have been considered as potential replacements for precious metals. However, their activities for water electrolysis are impeded by the strong hydrogen adsorption and low water adsorption energies. Herein, V-doped bimetallic nitrides, V-FeNi₃N/Ni₃N heterostructure, are synthesized via a hydrothermal-nitridation protocol and used as electrocatalysts for water splitting and urea electrolysis. The V-FeNi₃N/Ni₃N electrode exhibits superior HER and OER activities, and the overpotentials are 62 and 230 mV to acquire a current density of 10 mA cm^-2, respectively. Moreover, as a bifunctional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.54 V to reach a current density of 10 mA cm^-2. The continuous electrolysis can be run for more than 120 h, surpassing most previously reported electrocatalysts. The excellent performance for water electrolysis is dominantly due to V-doping and interface engineering, which could enhance water adsorption and regulate the adsorption/desorption of intermediates species, thereby accelerating HER and OER kinetic processes. Besides, a urea-assisted two-electrode electrolyzer for electrolytic hydrogen production requires a cell voltage of 1.46 V at 10 mA cm^-2, which is 80 mV lower than that of traditional water electrolysis.

Hydrogen production coupled with water and organic oxidation based on layered double hydroxides

Hydrogen production via electrochemical water splitting is one of the most green and promising ways to produce clean energy and address resource crisis, but still suffers from low efficiency and high cost mainly due to the sluggish oxygen evolution reaction (OER) process. Alternatively, electrochemical hydrogen-evolution coupled with alternative oxidation (EHCO) has been proposed as a considerable strategy to improve hydrogen production efficiency combined with the production of high value-added chemicals. Although with these merits, high-efficient electrocatalysts are always needed in practical operation. Typically, layered double hydroxides (LDHs) have been developed as a large class of advanced electrocatalysts toward both OER and EHCO with high efficiency and stability. In this review, we have summarized the latest progress of hydrogen production from the perspectives of designing efficient LDHs-based electrocatalysts for OER and EHCO. Particularly, the influence of structure design and component regulation on the efficiency of their electrocatalytic process have been discussed in detail. Finally, we look forward to the challenges in the field of hydrogen production via electrochemical water splitting coupled with organic oxidation, such as the mechanism, selected oxidation as well as system design, hoping to provide certain inspiration for the development of low-cost hydrogen production technology.

Targeted Regulation of the Electronic States of Nickel Toward the Efficient Electrosynthesis of Benzonitrile and Hydrogen Production

Highly efficient electro-oxidation of benzylamine to generate value-added chemicals coupled with the hydrogen evolution reaction (HER) is crucial but challenging. Herein, targeted regulation of the electronic states of Ni sites was realized via simple yet precise nitridation engineering. Benefiting from the insertion of N atoms into the Ni lattice, the Ni₃N electrode exhibits superior activity, selectivity, and stability for the benzylamine oxidation reaction (BOR). Especially, under the industrially relevant current (∼250 mA), the Ni₃N catalyst remains ∼95% selective for benzonitrile production, reaching 1.43 mmol h^-1 cm^-2. Experimental and theoretical findings reveal that the formation of Ni-N bonds upshifts the Ni d-band center and optimizes the electrophilic properties of Ni sites, which contributes to the adsorption and dehydrogenations process of benzylamine. Furthermore, due to the work function difference between Ni and Ni₃N, a strong mutual interaction occurs at the heterogeneous interface for Ni-Ni₃N, which endows it with the appropriate H* adsorption energy and thus excellent HER performance. Impressively, the integrated solar-energy-driven BOR coupled with the HER electrolyzer affords 10 mA cm^-2 at an ultralow voltage of 1.4 V and exhibits a promising practical application (η_{solar-to-hydrogen} = 13.8%). This work offers a new perspective for the bifunctional design of nitrides in the field of electrosynthesis.

The Role of Surface Curvature in Electrocatalysts

Excessive consumption of fossil fuels has caused unavoidable environmental problems. The development of renewable and clean alternatives is essential for the sustainable and green development of human society. Electrocatalysts are most important parts in these energy-related devices. Recently, scientists found that the surface curvature of electrocatalysts could play an important role for the improvement of catalytic performance and the optimization of intrinsic catalytic activity during electrocatalytic process. The role of surface curvature in electrocatalysts is still under investigating. In this minireview, we summarized the latest progress of electrocatalysts with different surface curvatures and their applications in energy-related applications. This review mainly involves the strategies for preparation of electrocatalysts with different surface curvatures, three typical electrocatalysts with different surface curvatures (curled surface, onion-like structure, and spiral structure), and the potential mechanisms that surface curvature in electrocatalysts affects activities.

Fabrication of hierarchical MoO3@NixCo2x(OH)6x core-shell arrays on carbon cloth as enhanced-performance electrodes for asymmetric supercapacitors

Advanced integrated electrode materials with designedcore-shell nanostructureplay a crucial role for the application in alternative energy storage system. Herein, hierarchical MoO₃@Ni_xCo_2x(OH)_6x core-shell arrays were equably grown on face of carbon cloth after a series of hydrothermal growth and electrochemical deposition processes. This core-shell arrays structure can not only provide large electroactive surface areas and high speed ion transport paths, but also keep the material structure stable during the process of redox reactions. Thus MoO₃@Ni_xCo_2x(OH)_6x displays excellent electrochemical performance (4.7 F cm^-2 at 10 mA cm^-2). Moreover, the asymmetric supercapacitor is assembled with MoO₃@Ni_xCo_2x(OH)_6x and carbon nanotubes, which delivers a maximal energy density of 0.50 mWh cm^-2 at 4.25 mW cm^-2, high specific capacitance and superior cycling stability (94.5% capacitance retention after 5000 cycles). We believe that MoO₃@Ni_xCo_2x(OH)_6x arrays could be a great prospective candidate energy storage materials.

Nitrogen-Doped Cobalt Diselenide with Cubic Phase Maintained for Enhanced Alkaline Hydrogen Evolution

The introduction of heteroatoms is one of the most important ways to modulate the intrinsic electronic structure of electrocatalysts to improve their catalytic activity. However, for transition metal chalcogenides with highly symmetric crystal structure (HS-TMC), the introduction of heteroatoms, especially those with large atomic radius, often induces large lattice distortion and vacancy defects, which may lead to structural phase transition of doped materials or structural phase reconstruction during the catalytic reaction. Such unpredictable situations will make it difficult to explore the connection between the intrinsic electronic structure of doped catalysts and catalytic activity. Herein, taking thermodynamically stable cubic CoSe₂ phase as an example, we demonstrate that nitrogen incorporation can effectively regulate the intrinsic electronic structure of HS-TMC with structural phase stability and thus promote its electrocatalytic activity for the hydrogen evolution activity (HER). In contrast, the introduction of phosphorus can lead to structural phase transition from cubic CoSe₂ to orthorhombic phase, and the structural phase of phosphorus-doped CoSe₂ is unstable for HER.

Ultrathin NiSe Nanosheets on Ni Foam for Efficient and Durable Hydrazine-Assisted Electrolytic Hydrogen Production

Hydrazine-assisted electrochemical water splitting is an important avenue toward low cost and sustainable hydrogen production. An efficient and stable bifunctional electrocatalyst for the hydrogen evolution reaction (HER) and the anodic hydrazine oxidation reaction (HzOR) is fundamental to this goal. Herein, we employed a facile method to fabricate ultrathin NiSe nanosheet arrays on nickel foam (NiSe/NF), which exhibits predominant electrocatalytic activity for both HER and HzOR. Our investigations revealed that the excellent electrocatalytic activity of the NiSe/NF mainly arises from the abundant electrocatalytic active sites endowed by the ultrathin nanosheet morphology, the rugged feature of the extended (100) nanosheet surface, the rich presence of Se on the nanosheet surface, and the three-dimensional (3D) porous structure of the NF and other factors such as high conductivity of the NiSe/NF and strong NiSe-NF adhesion. We assembled a hydrazine-boosted electrochemical water splitting cell using NiSe/NF as a bifunctional catalyst for both of the electrodes, and the constructed cell exhibits an ultralow overpotential (310 mV at 10 mA cm^-2), which is robust for 30 h continuous electrolysis in a 1 M KOH electrolyte. This work provides a promising avenue toward low cost, high-efficiency, and stable hydrogen production based on hydrazine-assisted electrolytic water splitting for future.

Energy-saving hydrogen production by chlorine-free hybrid seawater splitting coupling hydrazine degradation

Seawater electrolysis represents a potential solution to grid-scale production of carbon-neutral hydrogen energy without reliance on freshwater. However, it is challenged by high energy costs and detrimental chlorine chemistry in complex chemical environments. Here we demonstrate chlorine-free hydrogen production by hybrid seawater splitting coupling hydrazine degradation. It yields hydrogen at a rate of 9.2 mol h-1 gcat-1 on NiCo/MXene-based electrodes with a low electricity expense of 2.75 kWh per m3 H2 at 500 mA cm-2 and 48% lower energy equivalent input relative to commercial alkaline water electrolysis. Chlorine electrochemistry is avoided by low cell voltages without anode protection regardless Cl- crossover. This electrolyzer meanwhile enables fast hydrazine degradation to ~3 ppb residual. Self-powered hybrid seawater electrolysis is realized by integrating low-voltage direct hydrazine fuel cells or solar cells. These findings enable further opportunities for efficient conversion of ocean resources to hydrogen fuel while removing harmful pollutants.