Phase Segregation in Cu0.5Ni0.5 Alloy Boosting Urea-Assisted Hydrogen Production in Alkaline Media

Coupling urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is promising for energy-efficient hydrogen production. However, developing cheap and highly active bifunctional electrocatalysts for overall urea electrolysis remains challenging. In this work, a metastable Cu_0.5Ni_0.5 alloy is synthesized by a one-step electrodeposition method. It only requires the potentials of 1.33 and −28 mV to obtain the current density of ±10 mA cm⁻² for UOR and HER, respectively. The metastable alloy is considered to be the main reason causing the above excellent performances. In the alkaline medium, the as-prepared Cu_0.5Ni_0.5 alloy exhibits good stability for HER; and conversely, NiOOH species can be rapidly formed during the UOR due to the phase segregation of Cu_0.5Ni_0.5 alloy. In particular, for the energy-saving hydrogen generation system coupled with HER and UOR, only 1.38 V of voltage is needed at 10 mA cm⁻²; and at 100 mA cm⁻², the voltage decreases by ≈305 mV compared with that of the routine water electrolysis system (HER || OER). Compared with some catalysts reported recently, the Cu_0.5Ni_0.5 catalyst owns superior electrocatalytic activity and durability. Furthermore, this work provides a simple, mild, and rapid method for designing highly active bifunctional electrocatalysts toward urea-supporting overall water splitting.     

Exploring The Synergistic Effect Of CoSeP/CoP Interface Catalyst For Efficient Urea Electrolysis

Electrocatalytic oxidation of urea (UOR) is a potential energy-saving hydrogen production technology that can replace oxygen evolution reaction (OER). Therefore, CoSeP/CoP interface catalyst is synthesized on nickel foam using hydrothermal, solvothermal, and in situ template methods. The strong interaction of tailored CoSeP/CoP interface promotes the hydrogen production performance of electrolytic urea. During the hydrogen evolution reaction (HER), the overpotential can reach 33.7 mV at 10 mA cm⁻². The cell voltage can reach 1.36 V at 10 mA cm⁻² in the overall urea electrolytic process. Notably, the overall urine electrolysis performance of the catalyst in the human urine medium can reach 1.40 V at 10 mA cm⁻² and can exhibit durable cycle stability at 100 mA cm⁻². Density functional theory (DFT) proves that the CoSeP/CoP interface catalyst can better adsorb and stabilize reaction intermediates CO* and NH* on its surface through a strong synergistic effect, thus enhancing the catalytic activity.     

Rational Synthesis of Core-Shell-Structured Nickel Sulfide-Based Nanostructures for Efficient Seawater Electrolysis

Versatile electrocatalysis at higher current densities for natural seawater splitting to produce hydrogen demands active and robust catalysts to overcome the severe chloride corrosion, competing chlorine evolution, and catalyst poisoning. Hereto, the core-shell-structured heterostructures composed of amorphous NiFe hydroxide layer capped Ni₃S₂ nanopyramids which are directly grown on nickel foam skeleton (NiS@LDH/NF) are rationally prepared to regulate cooperatively electronic structure and mass transport for boosting oxygen evolution reaction (OER) performance at larger current densities. The prepared NiS@LDH/NF delivers the anodic current density of 1000 mA cm⁻² at the overpotential of 341 mV in 1.0 m KOH seawater. The feasible surface reconstruction of Ni₃S₂-FeNi LDH interfaces improves the chemical stability and corrosion resistance, ensuring the robust electrocatalytic activity in seawater electrolytes for continuous and stable oxygen evolution without any hypochlorite production. Meanwhile, the designed Ni₃S₂ nanopyramids coated with FeNi₂P layer (NiS@FeNiP/NF) still exhibit the improved hydrogen evolution reaction (HER) activity in 1.0 m KOH seawater. Furthermore, the NiS@FeNiP/NF||NiS@LDH/NF pair requires cell voltage of 1.636 V to attain 100 mA cm⁻² with a 100% Faradaic efficiency, exhibiting tremendous potential for hydrogen production from seawater.     

Key Roles of Interfacial OH− ion Distribution on Proton Coupled Electron Transfer Kinetics Toward Urea Oxidation Reaction

Enhancing alkaline urea oxidation reaction (UOR) activity is essential to upgrade renewable electrolysis systems. As a core step of UOR, proton-coupled electron transfer (PCET) determines the overall performance, and accelerating its kinetic remains a challenge. In this work, a newly raised electrocatalyst of NiCoMoCuO_xH_y with derived multi-metal co-doping (oxy)hydroxide species during electrochemical oxidation states is reported, which ensures considerable alkaline UOR activity (10/500 mA cm⁻² at 1.32/1.52 V vs RHE, respectively). Impressively, comprehensive studies elucidate the correlation between the electrode-electrolyte interfacial microenvironment and the electrocatalytic urea oxidation behavior. Specifically, NiCoMoCuO_xH_y featured with dendritic nanostructure creates a strengthened electric field distribution. This structural factor prompts the local OH⁻ enrichment in electrical double layer (EDL), so that the dehydrogenative oxidation of the catalyst is directly reinforced to facilitate the subsequent PCET kinetics of nucleophilic urea, resulting in high UOR performance. In practical utilization, NiCoMoCuO_xH_y-driven UOR coupled cathodic hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO₂RR), and harvested high value-added products of H₂ and C₂H₄, respectively. This work clarifies a novel mechanism to improve electrocatalytic UOR performance through structure-induced interfacial microenvironment modulation.     

3D Nitrogen‐Anion‐Decorated Nickel Sulfides for Highly Efficient Overall Water Splitting

Developing non‐noble‐metal electrocatalysts with high activity and low cost for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of paramount importance for improving the generation of H₂ fuel by electrocatalytic water‐splitting. This study puts forward a new N‐anion‐decorated Ni₃S₂ material synthesized by a simple one‐step calcination route, acting as a superior bifunctional electrocatalyst for the OER/HER for the first time. The introduction of N anions significantly modifies the morphology and electronic structure of Ni₃S₂, bringing high surface active sites exposure, enhanced electrical conductivity, optimal HER Gibbs free‐energy (ΔG_H*), and water adsorption energy change (ΔG_H2O*). Remarkably, the obtained N‐Ni₃S₂/NF 3D electrode exhibits extremely low overpotentials of 330 and 110 mV to reach a current density of 100 and 10 mA cm^?2 for the OER and HER in 1.0 m KOH, respectively. Moreover, an overall water‐splitting device comprising this electrode delivers a current density of 10 mA cm^?2 at a very low cell voltage of 1.48 V. Our finding introduces a new way to design advanced bifunctional catalysts for water splitting.     

Solvothermal synthesis of hybrid nanoarchitectonics nickel-metal organic framework modified nickel foam as a bifunctional electrocatalyst for direct urea and nitrate fuel cell

Urea and nitrate-based fuel cells have emerged as promising electricity generation devices. However, most of these catalysts are expensive and limited in supply, which limits their practical applications. Hence, metal-organic frameworks (MOF) have been explored as catalysts due to their low cost, easy preparation, and high redox activity. Here, we synthesize nickel-based MOF (Ni-MOF) via one-pot solvothermal technique as bifunctional electrocatalyst for the direct urea and nitrate fuel cell. The as-synthesized Ni-MOF is deposited on nickel foam (NF) and used as working electrode (Ni-MOF/NF) which demonstrates a peak current density of 188 mA/cm² for urea oxidation reaction (UOR) and −14 mA/cm² for nitrate reduction reaction (NRR) at an onset potential of ∼ 1.58 V (vs RHE), and ∼ 1.12 V (vs RHE), respectively The enhanced functionality of the Ni-MOF/NF electrode can be attributed to the high catalytic efficacy of the Ni-MOF. This is mainly due to the presence of multiple oxidation states of N (i.e., Ni^2+/3+) and excellent electronic conductivity of the organic ligands in MOF structure. Moreover, Ni-MOF/NF electrodes retain ∼ 71.2% and ∼ 83.9% capacity after 20000 s of UOR and NRR, respectively. This efficacy of the as-fabricated electrocatalyst proves MOF as a promising platform for direct fuel cell applications.     

Incorporating Nitrogen‐Doped Graphene Quantum Dots and Ni3S2 Nanosheets: A Synergistic Electrocatalyst with Highly Enhanced Activity for Overall Water Splitting

A noble‐metal‐free electrocatalyst is fabricated via in situ formation of nanocomposite of nitrogen‐doped graphene quantum dots (NGQDs) and Ni₃S₂ nanosheets on the Ni foam (Ni₃S₂‐NGQDs/NF). The resultant Ni₃S₂‐NGQDs/NF can serve as an active, binder‐free, and self‐supported catalytic electrode for direct water splitting, which delivers a current density of 10 mA cm^?2 at an overpotential of 216 mV for oxygen evolution reaction and 218 mV for hydrogen evolution reaction in alkaline media. This bifunctional electrocatalyst enables the construction of an alkali electrolyzer with a low cell voltage of 1.58 V versus reversible hydrogen electrode (RHE) at 10 mA cm^?2. The experimental results and theoretical calculations demonstrate that the synergistic effects of the constructed active interfaces are the key factor for excellent performance. The nanocomposite of NGQDs and Ni₃S₂ nanosheets can be promising water splitting electrocatalyst for large‐scale hydrogen generation or other energy storage and conversion applications.     

Super-Hydrophilic Microporous Ni(OH)x/Ni3S2 Heterostructure Electrocatalyst for Large-Current-Density Hydrogen Evolution

Exploiting active and stable non-precious metal electrocatalysts for alkaline hydrogen evolution reaction (HER) at large current density plays a key role in realizing large-scale industrial hydrogen generation. Herein, a self-supported microporous Ni(OH)x/Ni₃S₂ heterostructure electrocatalyst on nickel foam (Ni(OH)x/Ni₃S₂/NF) that possesses super-hydrophilic property through an electrochemical process is rationally designed and fabricated. Benefiting from the super-hydrophilic property, microporous feature, and self-supported structure, the electrocatalyst exhibits an exceptional HER performance at large current density in 1.0 M KOH, only requiring low overpotential of 126, 193, and 238 mV to reach a current density of 100, 500, and 1000 mA cm⁻², respectively, and displaying a long-term durability up to 1000 h, which is among the state-of-the-art non-precious metal electrocatalysts. Combining hard X-rays absorption spectroscopy and first-principles calculation, it also reveals that the strong electronic coupling at the interface of the heterostructure facilitates the dissociation of H₂O molecular, accelerating the HER kinetics in alkaline electrolyte. This work sheds a light on developing advanced non-precious metal electrocatalysts for industrial hydrogen production by means of constructing a super-hydrophilic microporous heterostructure.     

High-Performance Bifunctional Porous Iron-Rich Phosphide/Nickel Nitride Heterostructures for Alkaline Seawater Splitting

Seawater is the most abundant natural water resource in the world, which is an inexhaustible and low-cost feedstock for hydrogen production by alkaline water electrolysis. It is appearling to develop robust and stable electrocatalysts for alkaline seawater electrolysis. However, the development of seawater electrolysis is seriously impeded by anodic chloride corrosion and chlorine evolution reaction, and few non-noble electrocatalysts show prominent catalytic performance and excellent durability. Here, a heterogeneous electrocatalyst constructed by in situ growing highly dispersed iron-rich bimetallic phosphide nanoparticles on metallic Ni₃N (Fe_2−2xCo_2xP/Ni₃N), which exhibits outstanding bifunctional catalytic activities for alkaline seawater splitting, is reported. The optimal (Fe_0.74Co_0.26)₂P/Ni₃N and Fe₂P/Ni₃N electrocatalysts demand only 113 and 212 mV to afford 100 mA cm⁻² for hydrogen and oxygen evolution reactions (HER and OER) in 1 m KOH, respectively, thus substantially expediting overall water/seawater electrolysis at 100 mA cm⁻² with 1.592/1.645 V. Particularly, Fe₂P/Ni₃N displays an unprecedented overpotential of 302 mV at 500 mA cm⁻², which represents the best alkaline seawater oxygen evolution activity among the ever-reported non-noble electrocatalysts; and thus substantially expedites overall water/seawater splitting at 500 mA cm⁻² with 1.701/1.768 V, surpassing most of the reported non-noble lectrocatalysts. This work provides a new approach for developing high-performance electrocatalysts for seawater splitting.     

Nickel-Doped Carbon Dots as an Efficient and Stable Electrocatalyst for Urea Oxidation

Urea is a typical contaminant present in wastewater which may cause severe environmental problems. Electrochemical catalytic oxidation of urea has emerged as an efficient approach to solve this problem. Nevertheless, the current nickel-based catalysts (e.g., nickel hydroxide/sulfides) feature a high metal content. It not only lowers the utilization efficiency of nickel but also causes secondary pollution to the environment. Here, nickel-doped carbon dots (Ni-CDs) with an excellent and stable catalytic activity for the electrocatalytic urea oxidation reaction (UOR) are reported. Specifically, carbon dots (CDs) with abundant functional groups are synthesized by a one-pot hydrothermal method and then Ni-CDs with a very low metal content (1.1 at%) are prepared. The Ni²⁺ sites by coordination with carboxylic groups on the CDs provide excellent electrocatalytic activity and excellent durability for the UOR, as demonstrated by an anodic current density of 100 mA cm⁻² at a potential of 1.38 V (vs RHE) and similar experimental results in practical application. To the best of knowledge, this is the first report of CDs-based materials applied for the UOR, which opens an important new area of applicability for CDs as well as broadens the scope of the materials for electrochemical catalysis of urea.     

Fe-Regulated Amorphous-Crystal Ni(Fe)P2 Nanosheets Coupled with Ru Powerfully Drive Seawater Splitting at Large Current Density

Water electrolysis is an ideal method for industrial green hydrogen production. However, due to increasing scarcity of freshwater, it is inevitable to develop advanced catalysts for electrolyzing seawater especially at large current density. This work reports a unique Ru nanocrystal coupled amorphous-crystal Ni(Fe)P₂ nanosheet bifunctional catalyst (Ru-Ni(Fe)P₂/NF), caused by partial substitution of Fe to Ni atoms in Ni(Fe)P₂, and explores its electrocatalytic mechanism by density functional theory (DFT) calculations. Owing to high electrical conductivity of crystalline phases, unsaturated coordination of amorphous phases, and couple of Ru species, Ru-Ni(Fe)P₂/NF only requires overpotentials of 375/295 and 520/361 mV to drive a large current density of 1 A cm⁻² for oxygen/hydrogen evolution reaction (OER/HER) in alkaline water/seawater, respectively, significantly outperforming commercial Pt/C/NF and RuO₂/NF catalysts. In addition, it maintains stable performance at large current density of 1 A cm⁻² and 600 mA cm⁻² for 50 h in alkaline water and seawater, respectively. This work provides a new way for design of catalysts toward industrial-level seawater splitting.     

Phosphorus-Modified Amorphous High-Entropy CoFeNiCrMn Compound as High-Performance Electrocatalyst for Hydrazine-Assisted Water Electrolysis

Exploiting highly active and bifunctional catalysts for both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) is a prerequisite for the hydrogen acquisition. High-entropy materials have received widespread attention in catalysis, but the high-performance bifunctional electrodes are still lacking. Herein, a novel P-modified amorphous high-entropy CoFeNiCrMn compound is developed on nickel foam (NF) by one-step electrodeposition strategy. The achieved CoFeNiCrMnP/NF delivers remarkable HER and HzOR performance, where the overpotentials as low as 51 and 268 mV are realized at 100 mA cm⁻². The improved cell voltage of 91 mV is further demonstrated at 100 mA cm⁻² by assessing CoFeNiCrMnP/NF in the constructed hydrazine-assisted water electrolyser, which is almost 1.54 V lower than the HER||OER system. Experimental results confirm the important role of each element in regulating the bifuncational performance of high-entropy catalysts. The main influencing elements seem to be Fe and Ni for HER, while the P-modification and Cr metal may contribute a lot for HzOR. These synergistic advantages help to lower the energy barriers and improve the reaction kinetics, resulting in the excellent bifunctional activity of the CoFeNiCrMnP/NF. The work offers a feasible strategy to develop self-supporting electrode with high-entropy materials for overall water splitting.     

Boosting Alkaline Hydrogen and Oxygen Evolution Kinetic Process of Tungsten Disulfide-Based Heterostructures by Multi-Site Engineering

Alkaline water electrolysis is an advanced technology for scalable H₂ production using surplus electricity from intermittent energy sources, but it remains challenging for non-noble electrocatalysts to split water into hydrogen and oxygen efficiently, especially for tungsten disulfide (WS₂)-based catalysts. Density functional theory calculations in combination with experimental study are used to establish a multi-site engineering strategy for developing robust WS₂-based hybrid electrocatalyst on mesoporous bimetallic nitride (Ni₃FeN) nanoarrays for bifunctional water splitting. This ingenious design endows the catalyst with numerous edge sites chemically bonded with the conductive scaffold, which are favorable for water dissociation and hydrogen adsorption. Benefiting from the synergistic advantages, the N-WS₂/Ni₃FeN hybrid exhibits exceptional bifunctional properties for hydrogen and oxygen evolution reactions (HER and OER) in base with excellent large-current durability, requiring 84 mV to afford 10 mA cm^?2 for HER, and 240 mV at 100 mA cm^?2 for OER, respectively. Assembling the catalytic materials as both the anode and cathode to construct an electrolyzer, it is actualized very good activities for overall water splitting with only 1.5 V to deliver 10 mA cm^?2, outperforming the IrO₂⁽⁺⁾//Pt^(?) coupled electrodes and many non-noble bifunctional electrocatalysts thus far. This work provides a promising avenue for designing WS₂-based heterogeneous electrocatalysts for water electrolysis.     

Metal–Organic Framework–Derived Mesoporous B-Doped CoO/Co@N-Doped Carbon Hybrid 3D Heterostructured Interfaces with Modulated Cobalt Oxidation States for Alkaline Water Splitting (Small 35/2023)

Heteroatom-doped transition metal-oxides of high oxygen evolution reaction (OER) activities interfaced with metals of low hydrogen adsorption energy barrier for efficient hydrogen evolution reaction (HER) when uniformly embedded in a conductive nitrogen-doped carbon (NC) matrix, can mitigate the low-conductivity and high-agglomeration of metal-nanoparticles in carbon matrix and enhances their bifunctional activities. Thus, a 3D mesoporous heterostructure of boron (B)-doped cobalt-oxide/cobalt-metal nanohybrids embedded in NC and grown on a Ni foam substrate (B-CoO/Co@NC/NF) is developed as a binder-free bifunctional electrocatalyst for alkaline water-splitting via a post-synthetic modification of the metal–organic framework and subsequent annealing in different Ar/H₂ gas ratios. B-CoO/Co@NC/NF prepared using 10% H₂ gas (B-CoO/Co@NC/NF [10% H₂]) shows the lowest HER overpotential (196 mV) and B-CoO/Co@NC/NF (Ar), developed in Ar, shows an OER overpotential of 307 mV at 10 mA cm⁻² with excellent long-term durability for 100 h. The best anode and cathode electrocatalyst-based electrolyzer (B-CoO/Co@NC/NF (Ar)(+)//B-CoO/Co@NC/NF (10% H₂)(−)) generates a current density of 10 mA cm⁻² with only 1.62 V with long-term stability. Further, density functional theory investigations demonstrate the effect of B-doping on electronic structure and reaction mechanism of the electrocatalysts for optimal interaction with reaction intermediates for efficient alkaline water-splitting which corroborates the experimental results.     

Sulfur-Induced Low Crystallization of Ultrathin Pd Nanosheet Arrays for Sulfur Ion Degradation-Assisted Energy-Efficient H2 Production

The utilization of thermodynamically favorable sulfur oxidation reaction (SOR) as an alternative to sluggish oxygen evolution reaction is a promising technology for low-energy H₂ production while degrading the sulfur source from wastewater. Herein, amorphous/crystalline S-doped Pd nanosheet arrays on nickel foam (a/c S-Pd NSA/NF) is prepared by S-doping crystalline Pd NSA/NF.  Owing to the ultrathin amorphous nanosheet structure and the incorporation of S atoms, the a/c S-Pd NSA/NF provides a large number of active sitesand the optimized electronic structure, while exhibiting outstanding electrocatalytic activity in hydrogen evolution reaction (HER) and SOR. Therefore, the coupling system consisting of SOR-assisted HER can reach a current density of 100 mA cm⁻² at 0.642 V lower than conventional electrolytic water by 1.257 V, greatly reducing energy consumption. In addition, a/c S-Pd NSA/NF can generate H₂ over a long period of time while degrading S²⁻ in water to the value-added sulfur powder, thus further reducing the cost of H₂ production. This work proposes an attractive strategy for the construction of an advanced electrocatalyst for H₂ production and utilization of toxic sulfide wastewater by combining S-doping induced partial amorphization and ultrathin metal nanosheet arrays.     

IrPd Nanoalloy-Structured Bifunctional Electrocatalyst for Efficient and pH-Universal Water Splitting

The lack of high efficiency and pH-universal bifunctional electrocatalysts for water splitting to hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) hinders the large-scale production of green hydrogen. Here, an IrPd electrocatalyst supported on ketjenblack that exhibits outstanding bifunctional performance for both HER and OER at wide pH conditions is presented. The optimized IrPd catalyst exhibits a specific activity of 4.46 and 3.98 A mg_Ir⁻¹ in the overpotential of 100 and 370 mV for HER and OER, respectively, in alkaline conditions. When applied to the anion exchange membrane electrolyzer, the Ir₄₄Pd₅₆/KB catalyst shows a stability of >20 h at a current of 250 mA cm⁻² for water decomposition, indicating promising prospects for practical applications. Beyond offering an advanced electrocatalyst, this work also guides the rational design of desirable bifunctional electrocatalysts for HER and OER by regulating the microenvironments and electronic structures of metal catalytic sites for diverse catalysis.     

Hydroxyapatite-Derived Heterogeneous Ru-Ru2P Electrocatalyst and Environmentally-Friendly Membrane Electrode toward Efficient Alkaline Electrolyzer

Alkaline membrane water electrolysis is a promising production technology, and advanced electrocatalyst and membrane electrode design have always been the core technology. Herein, an ion-exchange method and an environmentally friendly in situ green phosphating strategy are successively employed to fabricate Ru-Ru₂P heterogeneous nanoparticles by using hydroxyapatite (HAP) as a phosphorus source, which is an exceptionally active electrocatalyst for hydrogen evolution reaction (HER). Density functional theory calculation results reveal that strong electronic redistribution occurs at the heterointerface of Ru-Ru₂P, which modulates the electronic structure to achieve an optimized hydrogen adsorption strength. The obtained Ru-Ru₂P possesses excellent HER performance (24 mV at 10 mA cm⁻²) and robust stability (1000 mA cm⁻² for 120 h) in alkaline media. Furthermore, an environmentally friendly membrane electrode with a sandwich structure is assembled by HAP nanowires as an alkaline membrane, Ru-Ru₂P as a cathodic catalyst, and NiFe-LDH as an anodic catalyst, respectively. The voltage of (−) Ru-Ru₂P || NiFe-LDH/CNTs (+) (1.53 V at 10 mA cm⁻²) is lower than that of (−) 20 wt% Pt/C || RuO₂ (+) (1.60 V at 10 mA cm⁻²) for overall water splitting. Overall, the studies not only design an efficient catalyst but also provide a new route to achieve a high-stability electrolyzer for industrial H₂ production.     

A Cost‐Efficient Bifunctional Ultrathin Nanosheets Array for Electrochemical Overall Water Splitting

The design of cost‐efficient earth‐abundant catalysts with superior performance for the electrochemical water splitting is highly desirable. Herein, a general strategy for fabricating superior bifunctional water splitting electrodes is reported, where cost‐efficient earth‐abundant ultrathin Ni‐based nanosheets arrays are directly grown on nickel foam (NF). The newly created Ni‐based nanosheets@NF exhibit unique features of ultrathin building block, 3D hierarchical structure, and alloy effect with the optimized Ni₅Fe layered double hydroxide@NF (Ni₅Fe LDH@NF) exhibiting low overpotentials of 210 and 133 mV toward both oxygen evolution reaction and hydrogen evolution reaction at 10 mA cm^?2 in alkaline condition, respectively. More significantly, when applying as the bifunctional overall water splitting electrocatalyst, the Ni₅Fe LDH@NF shows an appealing potential of 1.59 V at 10 mA cm^?2 and also superior durability at the very high current density of 50 mA cm^?2.     

Sequential Electrodeposition of Bifunctional Catalytically Active Structures in MoO3/Ni–NiO Composite Electrocatalysts for Selective Hydrogen and Oxygen Evolution

Exploring earth-abundant and highly efficient electrocatalysts is critical for further development of water electrolyzer systems. Integrating bifunctional catalytically active sites into one multi-component might greatly improve the overall water-splitting performance. In this work, amorphous NiO nanosheets coupled with ultrafine Ni and MoO₃ nanoparticles (MoO₃/Ni–NiO), which contains two heterostructures (i.e., Ni–NiO and MoO₃–NiO), is fabricated via a novel sequential electrodeposition strategy. The as-synthesized MoO₃/Ni–NiO composite exhibits superior electrocatalytic properties, affording low overpotentials of 62 mV at 10 mA cm⁻² and 347 mV at 100 mA cm⁻² for catalyzing the hydrogen and the oxygen evolution reaction (HER/OER), respectively. Moreover, the MoO₃/Ni–NiO hybrid enables the overall alkaline water-splitting at a low cell voltage of 1.55 V to achieve 10 mA cm⁻² with outstanding catalytic durability, significantly outperforming the noble-metal catalysts and many materials previously reported. Experimental and theoretical investigations collectively demonstrate the generated Ni–NiO and MoO₃–NiO heterostructures significantly reduce the energetic barrier and act as catalytically active centers for selective HER and OER, synergistically accelerating the overall water-splitting process. This work helps to fundamentally understand the heterostructure-dependent mechanism, providing guidance for the rational design and oriented construction of hybrid nanomaterials for diverse catalytic processes.     

Electronic Modulation Induced by Ni-VN Heterojunction Reinforces Electrolytic Hydrogen Evolution Coupled with Biomass Upgrade

The renewable electricity-driven hydrogen evolution reaction (HER) coupled with biomass oxidation is a powerful avenue to maximize the energy efficiency and economic feedback, but challenging. Herein, porous Ni-VN heterojunction nanosheets on nickel foam (Ni-VN/NF) are constructed as a robust electrocatalyst to simultaneously catalyze HER and 5-hydroxymethylfurfural electrooxidation reaction (HMF EOR). Benefiting from the surface reconstruction of Ni-VN heterojunction during the oxidation process, the derived NiOOH-VN/NF energetically catalyzes HMF into 2,5-furandicarboxylic acid (FDCA), yielding the high HMF conversion (>99%), FDCA yield (99%), and Faradaic efficiency (>98%) at the lower oxidation potential along with the superior cycling stability. Ni-VN/NF is also surperactive for HER, exhibiting an onset potential of ≈0 mV and Tafel slope of 45 mV dec⁻¹. The integrated Ni-VN/NF||Ni-VN/NF configuration delivers a compelling cell voltage of 1.426 V at 10 mA cm⁻² for the H₂O-HMF paired electrolysis, about 100 mV lower than that for water splitting. Theoretically, for Ni-VN/NF, the superiority in HMF EOR and HER is mainly dominated by the local electronic distribution at the heterogenous interface, which accelerates the charge transfer and optimize the adsorption of reactants/intermediates by modulating the d-band center, therefore being an advisable thermodynamic and kinetic process.