Hierarchical nanoporous Ni(Cu) alloy anchored on amorphous NiFeP as efficient bifunctional electrocatalysts for hydrogen evolution and hydrazine oxidation

Sub-3 nm 1 T-MoS2 self-supported nanosheets with fast ion transport and bubble release for membrane-free water electrolysis

Conventional water splitting is restricted by costly membrane electrode assemblies and a sluggish oxygen evolution reaction (OER) occurring at the anode. In light of this, the construction of a membrane-free water electrolysis system via a hydrazine-assisted seawater hydrogenation strategy surmounts both of these obstacles. Herein, we propose a new strategy to synthesize two-dimensional (2D) ultrathin porous 1 T-MoS2 (1 T-MoS2-10 %/CC), which consists of 2.3 nm triple-layer crystalline surface and has nano pores (2-4 nm). Due to the uniform and consistent nanosheet arrays composed of ultrathin large-layer-spacing nanosheets and abundant pores, the electrolyte and the 1 T-MoS2-10 %/CC can be fully contacted, showing superhydrophilicity, and increasing the bubble contact angle to release bubbles in time, showing superaerophobicity. Therefore, the special structure of 1 T-MoS2 shows advantageous for gas precipitation reaction-hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), which require only 55 mV overpotential for HER and 7 mV (vs. RHE) working potential for HzOR to achieve a current density of 10 mA cm-2. In addition, we constructed a hybrid seawater membrane-free electrolysis system in which a current density of 100 mA cm-2 can be achieve with a cell voltage of only 0.27 V, which not only effectively replaces the high-energy-consuming OER for energy-saving hydrogen production, but also avoids the electrochemical reaction of chlorine evolution reaction (ClER) with the low cell voltage.

Superhydrophilicity and superaerophobicity Ni/Ni3S4/1T-MoS2 for hydrazine-assisted seawater splitting

The overall hydrazine splitting (OHzS) is a promising strategy to achieve the efficient hydrogen production in seawater through replacing the slow kinetic oxygen evolution reaction (OER) and toxic chlorine evolution reaction (ClOR) by hydrazine oxidation (HzOR). We report an efficient bifunctional electrocatalyst of Ni/Ni3S4/1T-MoS2 on carbon cloth (Ni/Ni3S4/1T-MoS2/CC), which was formed from large layer spacing MoS2 and Ni3S4 with metal-Ni, and was applied as for both hydrogen evolution reaction (HER) and HzOR. The MoS2 had expanded interlayer spacing and showed 1T phase, with significantly improved conductivity and hydrophilicity, which promotes transfer process of reactants. Furthermore, the introduction of Ni/Ni3S4 on the 1T-MoS2 base surface leaded to superhydrophilic and superaerophobic properties, which makes it more conducive to the adsorption of H. The improvement of electrical conductivity induced the excellent HER and HzOR electrocatalytic properties of Ni/Ni3S4/1T-MoS2/CC, which showed an ultralow overpotential of 24 mV and working potential of 0 mV at a current density of 10 mA cm-2, respectively. Inspiringly, Ni/Ni3S4/1T-MoS2/CC also showed excellent performance in hydrazine-assisted alkaline seawater electrolysis, as well as solar panel powered electrolysis of seawater OHzS, therefore, exhibiting great potential for practical applications.

Lattice Strain Engineering of Ni2 P Enables Efficient Catalytic Hydrazine Oxidation-Assisted Hydrogen Production

Hydrazine-assisted water electrolysis provides new opportunities to enable energy-saving hydrogen production while solving the issue of hydrazine pollution. Here, the synthesis of compressively strained Ni2 P as a bifunctional electrocatalyst for boosting both the anodic hydrazine oxidation reaction (HzOR) and cathodic hydrogen evolution reaction (HER) is reported. Different from a multistep synthetic method that induces lattice strain by creating core-shell structures, a facile strategy is developed to tune the strain of Ni2 P via dual-cation co-doping. The obtained Ni2 P with a compressive strain of -3.62% exhibits significantly enhanced activity for both the HzOR and HER than counterparts with tensile strain and without strain. Consequently, the optimized Ni2 P delivers current densities of 10 and 100 mA cm-2 at small cell voltages of 0.16 and 0.39 V for hydrazine-assisted water electrolysis, respectively. Density functional theory (DFT) calculations reveal that the compressive strain promotes water dissociation and concurrently tunes the adsorption strength of hydrogen intermediates, thereby facilitating the HER process on Ni2 P. As for the HzOR, the compressive strain reduces the energy barrier of the potential-determining step for the dehydrogenation of *N2 H4 to *N2 H3 . Clearly, this work paves a facile pathway to the synthesis of lattice-strained electrocatalysts via the dual-cation co-doping.

Heteroatom-Induced Accelerated Kinetics on Nickel Selenide for Highly Efficient Hydrazine-Assisted Water Splitting and Zn-Hydrazine Battery

Hydrazine-assisted water electrolysis is a promising energy conversion technology for highly efficient hydrogen production. Rational design of bifunctional electrocatalysts, which can simultaneously accelerate hydrogen evolution reaction (HER)/hydrazine oxidation reaction (HzOR) kinetics, is the key step. Herein, we demonstrate the development of ultrathin P/Fe co-doped NiSe2 nanosheets supported on modified Ni foam (P/Fe-NiSe2) synthesized through a facile electrodeposition process and subsequent heat treatment. Based on electrochemical measurements, characterizations, and density functional theory calculations, a favorable "2 + 2" reaction mechanism with a two-step HER process and a two-step HzOR step was fully proved and the specific effect of P doping on HzOR kinetics was investigated. P/Fe-NiSe2 thus yields an impressive electrocatalytic performance, delivering a high current density of 100 mA cm-2 with potentials of - 168 and 200 mV for HER and HzOR, respectively. Additionally, P/Fe-NiSe2 can work efficiently for hydrazine-assisted water electrolysis and Zn-Hydrazine (Zn-Hz) battery, making it promising for practical application.

Prussian blue analog-derived nickel iron phosphide-reduced graphene oxide hybrid as an efficient catalyst for overall water electrolysis

Efficient and bifunctional nonprecious catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are essential for the production of green hydrogen via water electrolysis. Transition metal (Ni, Co, Fe, etc.) phosphides are frequently documented HER catalysts, whereas their bimetallic oxides are efficient OER catalysts, thus enabling bifunctional catalysis for water electrolysis via proper operation. Herein, phosphide-reduced graphene oxide (rGO) hybrids were prepared from graphene oxide (GO)-incorporated bimetal Prussian blue analog (PBA) precursors. The hybrids could experience partial surface oxidation to create oxide layers with OER activities, and the hybrids also possessed considerable HER properties, therefore enabling bifunctional catalytic features for water electrolysis. The typical NiFeP-rGO hybrid demonstrated an overpotential of 250 mV at 10 mA cm^-2 and good durability for OER, as well as moderate HER catalytic features (overpotential of 165 mV at -10 mA cm^-2 and acceptable catalytic stability). Due to the bifunctional catalytic features, the NiFeP-rGO-based symmetric water electrolyzer demonstrated a moderate input voltage and high faradaic efficiency (FE) for O₂ and H₂ production. The current work provides a feasible way to prepare OER and HER bifunctional catalysts by facile phosphorization of PBA-associated precursors and spontaneous surface oxidation. Given the oxidation/reduction bifunctional catalytic behaviors, phosphide-rGO hybrid catalysts have great potential for widespread application in fields beyond water electrolysis, such as electrochemical pollution abatement, sensors, energy devices and organic syntheses.

Hierarchical NiOx nanotube arrays/CoP nanosheets heterostructure enables robust alkaline hydrogen evolution reaction

Rational design of low-cost and high-efficiency electrocatalysts for hydrogen evolution reaction (HER) is critical for scalable and sustainable hydrogen production from economical water-alkali splitting. Herein, density functional theory (DFT) calculations reveal that coupling NiO_x and CoP could effectively boost overall HER kinetics through lowing the H₂O dissociation barrier, accelerating the OH* transfer process, and providing the rapid H* migration kinetics as well as the appropriate H* energetics. Based on these findings, we successfully prepared a three-dimensional (3D) self-supported electrode of ultrathin CoP nanosheets directly grown on the surface-oxidized Ni nanotube arrays via a simple and scalable electrochemical synthesis method. As expected, such a heterostructure electrode exhibits superior alkaline HER performance with low overpotentials of 51 and 164 mV to drive the current densities of 10 and 500 mA cm^-2, respectively, outperforming most of the efficient alkaline HER electrocatalysts.

In Situ Synthesis and Microfabrication of High Entropy Alloy and Oxide Compounds by Femtosecond Laser Direct Writing under Ambient Conditions

Synthesis and coating of multi-metal oxides (MMOs) and alloys on conductive substrates are indispensable to electrochemical applications, yet demand multiple, resource-intensive, and time-consuming processes. Herein, an alternative approach to the synthesis and coating of alloys and MMOs by femtosecond laser direct writing (FsLDW) is reported. A solution-based precursor ink is deposited and dried on the substrate and illuminated by a femtosecond laser. During the illumination, dried precursor ink is transformed to MMO/alloys and is simultaneously bonded to the substrate. The formulation of the alloy and MMO precursor ink for laser processing is universally applicable to a large family of oxides and alloys. The process is conducted at room temperature and in an open atmosphere. To demonstrate, a large family of 57 MMOs and alloys are synthesized from a group of 13 elements. As a proof of concept, Ni_0.24 Co_0.23 Cu_0.24 Fe_0.15 Cr_0.14 high entropy alloy synthesized on stainless-steel foil by FsLDW is used for the oxygen evolution reaction, which achieves a current density of 10 mA cm^-2 at a significantly low overpotential of 213 mV. Further, FsLDW can also achieve microfabrication of alloys/MMO with feature sizes down to 20 µm.

Manipulating the Water Dissociation Electrocatalytic Sites of Bimetallic Nickel-Based Alloys for Highly Efficient Alkaline Hydrogen Evolution

Transition-metal alloys are currently drawing increasing attention as promising electrocatalysts for the alkaline hydrogen evolution reaction (HER). However, traditional density-functional-theory-derived d-band theory fails to describe the hydrogen adsorption energy (ΔG_H ) on hollow sites. Herein, by studying the ΔG_H for a series of Ni-M (M=Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mo, W) bimetallic alloys, an improved d-band center was provided and a potential NiCu electrocatalyst with a near-optimal ΔG_H was discovered. Moreover, oxygen atoms were introduced into Ni-M (O-NiM) to balance the adsorption/desorption of hydroxyl species. The tailored electrocatalytic sites for water dissociation can synergistically accelerate the multi-step alkaline HER. The prepared O-NiCu shows the optimum HER activity with a low overpotential of 23 mV at 10 mA cm^-2 . This work not only broadens the applicability of d-band theory, but also provides crucial understanding for designing efficient HER electrocatalysts.

Bi-functional 3D-NiCu-Double Hydroxide@Partially Etched 3D-NiCu Catalysts for Non-Enzymatic Glucose Detection and the Hydrogen Evolution Reaction

Hydrogen production, which is in the spotlight as a promising eco-friendly fuel, and the need for inexpensive and accurate electronic devices in the biochemistry field are important emerging technologies. However, the use of electrocatalytic devices based on expensive noble metal catalysts limits commercial applications. In recent years, to improve performance and reduce cost, electrocatalysts based on cheaper copper or nickel materials have been investigated for the non-enzymatic glucose oxidation reaction (GOR) and hydrogen evolution reaction (HER). In this study, we demonstrate a facile and easy electrochemical method of forming a cheap nickel copper double hydroxide (NiCu-DH) electrocatalyst deposited onto a three-dimensional (3D) CuNi current collector, which can effectively handle two different reactions due to its high activity for both the GOR and the HER. The as-prepared electrode has a structure comprising abundant 3D-interconnected porous dendritic walls for easy access of the electrolyte ions and highly conductive networks for fast electron transfer; additionally, it provides numerous electroactive sites. The synergistic combination of the dendritic 3D-CuNi with its abundant active sites and the self-made NiCu-DH with its excellent electrocatalytic activity toward the oxidation of glucose and HER enables use of the catalyst for both reactions. The as-prepared electrode as a glucose sensor exhibits an outstanding glucose detection limit value (0.4 μM) and a wide detection range (from 0.4 μM to 1.4 mM) with an excellent sensitivity of 1452.5 μA/cm2/mM. The electrode is independent of the oxygen content and free from chloride poisoning. Furthermore, the as-prepared electrode also requires a low overpotential of -180 mV versus reversible hydrogen electrode to yield a current density of 10 mA/cm2 with a Tafel slope of 73 mV/dec for the HER. Based on this performance, this work introduces a new paradigm for exploring cost-effective bi-functional catalysts for the GOR and HER.

Cooperative effect of bimetallic MOF-derived CoNi(OH)2@NiCo2S4nanocomposite electrocatalysts with boosted oxygen evolution activity

Highly efficient and inexpensive electrocatalysts for oxygen evolution reaction (OER) are extensively studied for water splitting. Herein, a unique bimetallic nanocomposite CoNi(OH)₂@NiCo₂S₄nanosheet arrays derived from metal-organic-frameworks (MOFs, CoNi-ZIF) is simply fabricated on Ni foam, endowing large specific surface area and outstanding electrical conductivity. Compared with their single-metallic counterparts, the bimetallic composite displays dramatically low overpotential and small Tafel slope as well as outstanding catalytic stability. The overpoptential at 20 mA cm^-2for CoNi(OH)₂@NiCo₂S₄is only 230 mV in comparison with Ni(OH)₂@Ni₃S₂(266 mV), Co(OH)₂@Co₃S₄(294 mV) and RuO₂(η = 302 mV). First-principle calculations based on density functional theory (DFT) are carried out and reveal that the introduction of Ni in Co(OH)₂helps lowered the energy difference of ΔG_OOH*-ΔG_O*, and thereby boosting the OER reactivity. This study provides an effective approach for the rational construction of low-cost metal hybrids.

A Porous Tungsten Substrate for Catalytic Reduction of Hydrogen by Dealloying of a Tungsten–Rhenium Alloy in an Aqueous Solution of Hydrochloric Acid

Selective dissolution of a tungsten (85 wt.%)–rhenium (15 wt.%) alloy with rhenium in hydrochloric acid at the temperature of 298 K and anodic polarization modes was carried out to develop a porous catalytic substrate and to recycle rare metals. The parameters of the effective selective anodic dissolution of the tungsten–rhenium alloy, including the differences in applied potentials and electrolyte composition, were found. It was established that samples of the tungsten–rhenium alloy possess the smallest average pore size after being exposed for 6000 s. The obtained porous tungsten samples were characterized by X-ray diffraction and scanning electron spectroscopy. A thermodynamic description of the processes occurring during the anodic selective dissolution of a binary alloy was proposed. In the course of the work, the selectivity coefficient was determined using an X-ray fluorescence wave-dispersion spectrometer XRF-1800. The existence of a bimodal structure on the tungsten surface after dealloying was proved.

Amorphous materials for elementary-gas-involved electrocatalysis: an overview

Given the critical demands on energy conversion, storage, and transportation, tremendous interest has been devoted to the field of material development related to energy harvesting, recently. As the only route towards energy utilization, the carriers with the characteristics of low carbon are regarded as the future choice, e.g., hydrogen and ammonia. To this end, electrocatalysis provides a green way to access these substances. However, the unfulfilled conversion efficiency is the bottleneck for practical application. In this review, the promising characteristics of amorphous materials and the amorphous-induced electrocatalytic enhancement (AIEE) were emphasized. In the beginning, the characteristics of amorphous materials are briefly summarized. The basic mechanism of heterogeneous electrocatalytic reactions is illustrated, including the hydrogen/oxygen evolution and oxygen/nitrogen reduction. In the third part, the electrocatalytic performance of amorphous materials is discussed in detail, and the mechanism of AIEE is highlighted. In the last section of this review, the challenges and outlook for the development of amorphous enhanced electrocatalysis are presented.

FeNiP nanoparticle/N,P dual-doped carbon composite as a trifunctional catalyst towards high-performance zinc-air batteries and overall water electrolysis

A composite catalyst with a novel construction of bimetallic phosphide FeNiP nanoparticles embedded in an N,P double-doped carbon matrix was prepared. It was demonstrated to be a trifunctional catalyst that can efficiently catalyze the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It was found that the introduction of oleylamine during the preparation can adjust the catalytic sites and finally lead to ideal catalytic performances. The obtained catalyst exhibited efficient ORR catalytic performance that surpassed the commercial Pt/C catalyst, with the OER performance comparable to that of RuO₂ as well as excellent HER performance. The ORR half-wave potential is 0.879 V (vs. RHE) in 0.1 M KOH solution, while the OER overpotential at a current density of 10 mA cm^-2 is only 280 mV in 1 M KOH solution. The potential gap between the ORR and OER was only 0.700 V in 0.1 M KOH solution. This trifunctional catalyst was further evaluated in energy devices including zinc-air batteries and water electrolysis. The liquid zinc-air battery assembly achieved a power density of 169 mW cm^-2 and stably undergoes charge-discharge cycles for 210 hours. The solid-state zinc-air battery achieved a power density of 70 mW cm^-2 and stably undergoes charge-discharge cycles for 40 hours. These performances surpassed the batteries assembled with a Pt/C-RuO₂ mixed catalyst. This work established a foundation of composite catalysts coupled with bimetallic phosphide and hybrid carbon substrates, which will promote the development of high-performance multifunctional catalysts and their application in energy devices.

Boosting Hydrazine Oxidation Reaction on CoP/Co Mott-Schottky Electrocatalyst through Engineering Active Sites

The hydrazine oxidation reaction (HzOR), as a substitute for the sluggish oxygen evolution reaction (OER), is identified as a promising powerfrugal strategy for hydrogen production through water splitting. However, the HzOR activity of the present electrocatalysts is unsatisfying because the work potential is much higher than the theoretical value. Herein, we design a typical Mott-Schottky electrocatalyst consisting of CoP/Co nanoparticles for the HzOR, which exhibits remarkable HzOR activity with ultralow potentials of -69 and 177 mV at 10 and 100 mA cm^-2, respectively. It stands out in a range of cobalt-based materials and is even comparable to some precious-metal-based materials composed of Pt or Ru. A shown by with structural characterization and density functional theory (DFT) calculations, the interfaces between CoP/Co nanoparticles not only provide the active sites of HzOR but also promote the multistep dehydrogenation reaction of N₂H₄, thus enhancing the HzOR activity.

Three-dimensional Nanoporous Cu-Doped Ni Coating as Bifunctional Electrocatalyst for Hydrazine Sensing and Hydrogen Evolution Reaction

Developing a cost-effective and efficient bifunctional electrocatalyst with simple synthesis strategy for hydrazine sensing and H evolution reaction (HER) is of utmost importance. Herein, a three-dimensional porous Cu-doped metallic Ni coating on Ti mesh (Ni(Cu) coating/TM) was successfully electrodeposited by a facile electrochemical method. Electrochemical etching of the electrodeposited Ni(Cu) coating with metallic Ni and Cu mixed phase on a Ti mesh contributed to the formation of a three-dimensional porous Cu-doped metallic Ni coating. Owing to the large specific surface area and enhanced electroconductivity caused by the porous structure and Cu doping, respectively, the developed Ni(Cu) coating/TM exhibited superior hydrazine sensing performance and electrocatalytic activity toward hydrogen evolution reaction (HER). The Ni(Cu) coating/TM electrode presented a good sensitivity of 3909μA mM^-1cm^-2and two relatively broad linear ranges from 0.004 mM to 2.915 mM and from 2.915 mM to 5.691 mM as well as a low detection limit of 1.90μM. In addition, the Ni(Cu) coating/TM required a relatively low HER overpotential of 140 mV to reach -10 mA cm^-2and exhibited robust durability in alkaline solution. The excellent hydrazine electrooxidation and HER performance guarantee its promising application in hydrazine detection and energy conversion.

Superhydrophilic Ni-based Multicomponent Nanorod-Confined-Nanoflake Array Electrode Achieves Waste-Battery-Driven Hydrogen Evolution and Hydrazine Oxidation

The low thermodynamic potential (-0.33 V) and safe by-product of N₂ /H₂ O, make utilizing hydrazine oxidation reaction (HzOR) to replace thermodynamically-unfavorable and kinetically-sluggish oxygen evolution reaction a promising tactic for energy-efficient hydrogen production. However, the complexity of bifunctionality increases difficulties for effective material design, thus hindering the large-scale hydrogen generation. Herein, we present the rationally designed synthesis of superhydrophilic Ni-based multicomponent arrays (Ni NCNAs) composed of 1D nanorod-confined-nanoflakes (2D), which only needs -26 mV of working potential and 47 mV of overpotential to reach 10 mA cm^-2 for HzOR and HER, respectively. Impressively, this Ni NCNA electrode exhibits the top-level bifunctional activity for overall hydrazine splitting (OHzS) with an ultralow voltage of 23 mV at 10 mA cm^-2 and a record-high current density of 892 mA cm^-2 at just 0.485 V, also achieves the high-speed hydrogen yield driven by a waste AAA battery for OHzS.

Dual-functioning porous catalysts: robust electro-oxidation of small organic molecules and water electrolysis using bimetallic Ni/Cu foams

The simultaneous co-deposition of Cu within the matrix of Ni foams (utilizing DHBT) increases their intrinsic catalytic activity towards water electrolysis, urea oxidation reaction (UOR), and glycerol oxidation reaction (GOR) in alkaline media.

Nanostructured metal phosphides: from controllable synthesis to sustainable catalysis

Metal phosphides (MPs) with unique and desirable physicochemical properties provide promising potential in practical applications, such as the catalysis, gas/humidity sensor, environmental remediation, and energy storage fields, especially for transition metal phosphides (TMPs) and MPs consisting of group IIIA and IVA metal elements. Most studies, however, on the synthesis of MP nanomaterials still face intractable challenges, encompassing the need for a more thorough understanding of the growth mechanism, strategies for large-scale synthesis of targeted high-quality MPs, and practical achievement of functional applications. This review aims at providing a comprehensive update on the controllable synthetic strategies for MPs from various metal sources. Additionally, different passivation strategies for engineering the structural and electronic properties of MP nanostructures are scrutinized. Then, we showcase the implementable applications of MP-based materials in emerging sustainable catalytic fields including electrocatalysis, photocatalysis, mild thermocatalysis, and related hybrid systems. Finally, we offer a rational perspective on future opportunities and remaining challenges for the development of MPs in the materials science and sustainable catalysis fields.

Recent Progress on NiFe-Based Electrocatalysts for the Oxygen Evolution Reaction

The seriousness of the energy crisis and the environmental impact of global anthropogenic activities have led to an urgent need to develop efficient and green fuels. Hydrogen, as a promising alternative resource that is produced in an environmentally friendly and sustainable manner by a water splitting reaction, has attracted extensive attention in recent years. However, the large-scale application of water splitting devices is hindered predominantly by the sluggish oxygen evolution reaction (OER) at the anode. Therefore, the design and exploration of high-performing OER electrocatalysts is a critical objective. Considering their low prices, abundant reserves, and intrinsic activities, NiFe-based bimetal compounds are widely studied as excellent OER electrocatalysts. Moreover, recent progress on NiFe-based OER electrocatalysts in alkaline environments is comprehensively and systematically introduced through various catalyst families including NiFe-layered hydroxides, metal-organic frameworks, NiFe-based (oxy)hydroxides, NiFe-based oxides, NiFe alloys, and NiFe-based nonoxides. This review briefly introduces the advanced NiFe-based OER materials and their corresponding reaction mechanisms. Finally, the challenges inherent to and possible strategies for producing extraordinary NiFe-based electrocatalysts are discussed.

Partially exposed RuP2 surface in hybrid structure endows its bifunctionality for hydrazine oxidation and hydrogen evolution catalysis

Replacing the sluggish anode reaction in water electrolysis with thermodynamically favorable hydrazine oxidation could achieve energy-efficient H2 production, while the shortage of bifunctional catalysts limits its scale development. Here, we presented the scalable one-pot synthesis of partially exposed RuP2 nanoparticle-decorated carbon porous microsheets, which can act as the superior bifunctional catalyst outperforming Pt/C for both hydrazine oxidation reaction and hydrogen evolution reaction, where an ultralow working potential of -70 mV and an ultrasmall overpotential of 24 mV for 10 mA cm-2 can be achieved. The two-electrode electrolyzer can reach 10 mA cm-2 with a record-low cell voltage of 23 mV and an ultrahigh current density of 522 mA cm-2 at 1.0 V. The DFT calculations unravel the notability of partial exposure in the hybrid structure, as the exposed Ru atoms are the active sites for hydrazine dehydrogenation, while the C atoms exhibit a more thermoneutral value for H* adsorption.

Bifunctional nanoporous Ni-Zn electrocatalysts with super-aerophobic surface for high-performance hydrazine-assisted hydrogen production

In the present study, an effective approach is proposed to replace the oxygen evolution reaction with the substituted anodic hydrazine oxidation reaction (HzOR) to assist in hydrogen generation based on a bifunctional porous Ni-Zn electrocatalyst with nanosheet arrays. The Ni-Zn catalyst exhibits an extraordinary HzOR performance with a high current density of 970 mA cm^-2 at 0.7 V, and 93.8% of its initial activity after 5000 s, simultaneously delivering an overpotential of 68 mV at 10 mA cm^-2 for the hydrogen evolution reaction. Moreover, the electrolytic cell is constructed employing Ni-Zn catalysts as both the anode and cathode, achieving 100 mA cm^-2 at an ultralow cell voltage of 0.497 V with an outstanding stability over 10 h. The superior electrocatalytic performance can be ascribed to its porous structure with large active surface area, high electrical conductivity, and most importantly the super-aerophobic nature of the Ni-Zn surface. This work also provides a novel approach to designing and constructing porous structured non-noble metal bifunctional electrocatalysts with super-aerophobic surface to be used for energy-saving hydrogen production.

Modulation engineering of in situ cathodic activation of FePx based on W-incorporation for the hydrogen evolution reaction

In situ electrochemical activation as a new pretreating method to adjust electrocatalytic performance attracts extensive attention. However, the activation mechanisms of electrocatalysts are still ambiguous. Herein, we propose a facile modulation strategy of in situ cathodic activation of FeP_x based on W-incorporation (W-FeP_x/IF) for the hydrogen evolution reaction (HER). The activated W-FeO_x with obvious surface reconstruction demonstrates the role of W-incorporation for driving the cathodic activation of FeP_x, which suggests the larger surface area and more active sites. In fact, W incorporation can not only accelerate the cathodic activation process but also act as the adsorption sites for H_ad to form the synergistic effect with FeO_x for water dissociation. The obtained W-FeO_x/IF exhibits greatly enhanced HER activity featuring decreased overpotential from 237.7 to 154.0 mV at 100 mA cm^-2, which may be ascribed to W-FeO_x with double catalytic active sites after cathodic activation. Additionally, the modulation effects of cathodic activation can be exactly achieved by changing electrochemical parameters such as CV cycles. W-FeO_x/IF also shows excellent long-term stability for at least 100 h at 100 mA cm^-2. This modulation engineering based on metal doping is expected to provide inspiration for the understanding of the cathodic activation process for efficient electrocatalysts.

Manipulating dehydrogenation kinetics through dual-doping Co3N electrode enables highly efficient hydrazine oxidation assisting self-powered H2 production

Replacing sluggish oxygen evolution reaction (OER) with hydrazine oxidation reaction (HzOR) to produce hydrogen has been considered as a more energy-efficient strategy than water splitting. However, the relatively high cell voltage in two-electrode system and the required external electric power hinder its scalable applications, especially in mobile devices. Herein, we report a bifunctional P, W co-doped Co3N nanowire array electrode with remarkable catalytic activity towards both HzOR (-55 mV at 10 mA cm-2) and hydrogen evolution reaction (HER, -41 mV at 10 mA cm-2). Inspiringly, a record low cell voltage of 28 mV is required to achieve 10 mA cm-2 in two-electrode system. DFT calculations decipher that the doping optimized H* adsorption/desorption and dehydrogenation kinetics could be the underlying mechanism. Importantly, a self-powered H2 production system by integrating a direct hydrazine fuel cell with a hydrazine splitting electrolyzer can achieve a decent rate of 1.25 mmol h-1 at room temperature.

Uniform Loading of Nickel Phosphide Nanoparticles in Hierarchical Carbonized Wood Channel for Efficient Electrocatalytic Hydrogen Evolution

The development of self-supporting high-efficiency catalysts is a major challenge for the efficient production of H2 via water splitting. In this manuscript, a freestanding Ni2P-Ni12P5/carbonized wood (CW) composite electrode was prepared by a simple hydrothermal method and high-temperature calcination using pine wood with uniform channel as support and a large number of hydroxyl groups as nucleation center. The morphology and structural characteristics indicated that the Ni2P and Ni12P5 nanoparticles were uniformly distributed within the hierarchical porous structure of the CW. In acid media, the as-prepared Ni2P-Ni12P5/CW exhibits an excellent catalytic activity with a low overpotential of 151 mV at 10 mA cm−2 and a reasonably good long-term stability.

A bifunctional nanoporous Ni-Co-Se electrocatalyst with a superaerophobic surface for water and hydrazine oxidation

The sluggish kinetics of the oxygen evolution reaction (OER) has severely hindered the energetic convenience of water splitting. Thus, developing a highly efficient catalyst for the OER and replacing the OER with hydrazine oxidation (HzOR) are effective strategies for water electrolysis to achieve sustainable hydrogen production. Herein, bifunctional nanosheet arrays Ni0.6Co0.4Se with a porous structure were fabricated on Ni foam (NF) by the bubble dynamic template method during electrodeposition. Compared with CoSe2 and NiSe2, Ni0.6Co0.4Se exhibits excellent electrocatalytic performance for both the OER and HzOR. A low overpotential of only 249 mV is required to drive 10 mA cm-2, and a retention rate of nearly 100% after 24 h at 10 mA cm-2 is observed for Ni0.6Co0.4Se towards the OER. By substituting the OER by HzOR, an extremely high current density of 300 mA cm-2 at 0.4 V vs. RHE and a retention rate of 86.8% at 200 mA cm-2 after 12 h can be achieved. Interestingly, the mechanistic reason for the enhanced catalytic ability of Ni0.6Co0.4Se was studied, which is associated with the synergistic effects of Ni and Co, large ECSA, high electrical conductivity and most importantly the superaerophobic nature induced by the porous structure of Ni0.6Co0.4Se. The non-noble metal bifunctional electrocatalyst demonstrates a promising potential for application in both the OER and HzOR.

Porous nickel electrodes with controlled texture for the hydrogen evolution reaction and sodium borohydride electrooxidation

Porous Ni electrodes with different textures were successfully fabricated by electrodeposition in the presence of NH₄Cl and (NH₄)₂SO₄. Moreover, we studied the effect of texture on porous nickel electrodes for HER and NaBH₄ electrooxidation.

0.2 V Electrolysis Voltage-Driven Alkaline Hydrogen Production with Nitrogen-Doped Carbon Nanobowl-Supported Ultrafine Rh Nanoparticles of 1.4 nm

The development of highly effective and low-cost electrocatalysts for energy-saving hydrogen production via water splitting is still a great challenge. Herein, porous nitrogen-doped carbon nanobowls (N-CBs) have been designed and used for the controlled growth of ultrafine rhodium (Rh) nanoparticles. With the aid of interfacial bonding of Rh and N, ultrafine Rh nanoparticles with an average size of 1.4 nm have been successfully immobilized on the N-CBs. This Rh/N-CB electrocatalyst shows superior activity and high stability for the hydrogen evolution reaction (HER) and the hydrazine oxidation reaction (HzOR). More importantly, the Rh/N-CBs exhibit high activity for hydrogen production from water electrolysis, marking with a cell voltage of 0.2 V to achieve a current density of 20 mA cm^-2 when they serve as cathodic electrocatalysts for the HER and anodic electrocatalysts for the HzOR in 1 M KOH with 0.5 M hydrazine. The density functional theory calculations demonstrate that a near-zero hydrogen adsorption free energy produced by the chemical bonding of Rh with the pyrrole-N doped in N-CBs is responsible for the excellent HER activity of Rh/N-CBs electrocatalysts.