Hydrogen Evolution Reaction Current Density Research Articles

Engineering the Coordination Environment in the Silver(I)- and Ruthenium(II)-N-Heterocyclic Carbene Complexes in Instigating the Electrocatalytic Hydrogen Evolution Reaction.

The quest for cost-efficient and high-performance electrocatalysts towards electrocatalytic water splitting is a key and an interdisciplinary area of study. Considerable progress is being driven by developments in the field of energy research. In a fundamental study, we have synthesized NHC precursors (6 and 7) and corresponding metal-NHC complexes of silver(I)- (8 and 9) and ruthenium(II)- (10 and 11) of a N-heterocyclic carbene-based ligand type incorporating coumarins. These NHC precursors and metal-NHC complexes were characterized through various analytical and spectral techniques. The silver(I)-NHC complexes 8 and 9 displayed a linear coordination geometry with a center of inversion, which is evidenced by the single-crystal X-ray diffraction technique. Both the series of complexes were assessed for their efficacies in the hydrogen evolution reaction (HER). The results demonstrated that attributed to its peculiar coordination geometry, high electrical conductivity the silver(I)- and ruthenium(II)-NHC complexes exhibited exemplary electrocatalytic activity. Activities of the hydrogen evolution reaction on two differently modified electrode substrates with metal-NHC complexes have been studied. To attain the benchmark HER current density of 10 mA cm-2, in 1.0 M KOH, an overpotential of -375 to -527 mV vs RHE was required for the metal-NHC complexes. Based on the analysis of the Tafel slope values, the rate-determining step was the adsorption of hydrogen as investigated in the potential window. The molecular electrocatalyst 10 presented a superior stability and maintained the electrocatalytic activity for a duration of 18 h with complex 8 and 24 h with respect to complex 10 in 1.0 M KOH. Apace with these studies, hydrogen oxidation studies were examined in 0.5 M H2SO4 by a substantial current density at the platinum ring electrode. This research offers feasible guidance for developing organometallic-based molecular electrocatalysts with good electrocatalytic performance.

Electrodeposited NiB Films as Bifunctional Electrocatalysts in Alkaline Water Electrolizer

Abstract Sustainable electrochemical energy generation requires cost-effective, noble-metal-free electrocatalysts for hydrogen and oxygen production in electrolyzers. This study used electrodeposition to create crystalline NiB films with different boron (B) contents—Ni-B(1.17 wt.%), Ni-B(1.06 wt.%), Ni-B(0.94 wt.%), and Ni-B(0.89 wt.%)—on FTO substrates. These films were tested as bifunctional electrocatalyst electrodes for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline media. The NiB films' composition and morphology were analyzed using SEM, AFM, XRD, GD-OES, and XPS. Linear sweep voltammetry assessed their electrocatalytic performance. Higher B content in the films promoted the formation of electroactive NiOOH, enhancing the OER. The Ni-B(1.17 wt.%) electrode required an overpotential of 380 mV to reach 10 mA cm⁻² for OER, while the Ni-B(1.06 wt.%) electrode required 146 mV for the same current density for HER. An alkaline water electrolyzer using Ni-B(1.17 wt.%) as the anode and Ni-B(1.06 wt.%) as the cathode achieved a current density of 10 mA cm⁻² at 1.71 V for overall water splitting. The system showed stability over 12 hours of testing. The results indicate that NiB films on FTO substrates are promising, low-cost bifunctional electrocatalysts for alkaline water electrolysis, offering an alternative to noble-metal-based electrocatalysts.

Confining Flat Ru Islands into TiO2 Lattice with the Coexisting Ru-O-Ti and Ru-Ti Bonds for Ultra-Stable Hydrogen Evolution at Amperometric Current Density and Hydrogen Oxidation at High Potential.

Effective hydrogen evolution reaction (HER) under high current density and enhanced hydrogen oxidation reaction (HOR) over a wide potential range remain challenges for Ru-based electrocatalysts because its strong affinity to the adsorbed hydroxyl (OHad) inhibits the supply of the adsorbed hydrogen (Had). Herein, the coexisting RuOTi and Ru-Ti bonds are constructed by taking TiO2 crystal confined flat-Ru clusters (F-Ru@TiO2) to cope with above-mentioned obstacles. The different electronegativity (χTi = 1.54 < χRu = 2.20 < χO = 3.44) can endow Ti sites in RuOTi bonds with more positive charge and stabilize Ru atoms of RuTi bonds with the low-valence. The strength of Ru-OHad is then weakened by the oxophilicity of positively charged Ti atom in Ru-O-Ti bonds and the stronger Ti-OHad bond could release active Ru sites, especially for low-valence Ru in RuTi bonds, to serve as exclusive Had sites. As expected, F-Ru@TiO2 shows a low HER overpotential of 74 mV at 1000mA cm-2 and an ultrahigh mass activity of 3155A gRu -1 for HOR. More importantly, F-Ru@TiO2 can tolerate the HER current density of 1000mA cm-2 for 100h and the high anodic potential for HOR up to 0.5V versus RHE.

Bimetallic MOF derived Cu3P/Co2P grown on coal-based carbon fibers as self-supporting electrocatalyst for enhanced hydrogen evolution

Transition metal phosphides (TMPs) are often considered as a cost-effective replacement for precious metal catalysts in hydrogen evolution reaction (HER). Herein, the fibers are produced by combining coal with electrospinning technology, and then undergoing a pre-oxidation process for transforming into pre-oxidized coal-based fibers. Subsequently, CuCo-metal organic framework (CuCo-MOF) is grown on the pre-oxidized coal-based fibers using solvothermal method, and the Cu3P/Co2P/coal-based carbon fibers (Cu3P/Co2P/C-CFs) composite catalyst is successfully fabricated by phosphating at low temperature and carbonizing at high temperature. The uniformly grown nanoparticles (NPs) on the surface of C-CFs enhance the electrochemically active area, while the electron transfer between Cu3P and Co2P effectively modulates the electronic structure, increasing the catalytic activity of the catalyst for HER. In addition, the flexible C-CFs not only serve as self-supporting electrode but also effectively inhibit the agglomeration of Cu3P/Co2P NPs. Remarkably, the overpotential of Cu3P/Co2P/C-CFs is 83 mV at 10 mA cm−2 current density for HER in 0.5 mol L−1 H2SO4 solution. This study presents promising strategies for the high value-added utilization of coal and the synthesis of highly effective non-precious metal catalysts.

Cu-doped Ni3S2 electrocatalyst for glycerol oxidation coupling to promote hydrogen evolution reaction

Hydrogen energy is becoming increasingly important as a clean and efficient form of energy. Glycerol oxidation synergistic electrocatalytic hydrogen evolution technology is an electrochemical process that integrates anodic glycerol oxidation reaction (GOR) and cathodic hydrogen production. Compared with the oxygen evolution reaction (OER) required in the electrolysis of water for hydrogen production process, this technology can not only reduce the energy consumption of the whole reaction, but also obtain valuable by-products while producing hydrogen. In this study, we successfully prepared a copper-doped Ni3S2 (Cu-Ni3S2@NF) electrode material loaded on a nickel foam carrier by a two-stage hydrothermal synthesis method, and applied it to the bifunctional electrocatalytic reaction of GOR and hydrogen evolution reaction (HER). After a series of in-depth electrochemical performance tests, it was confirmed that 0.1Cu-Ni3S2@NF showed lower overpotential requirements when performing GOR and HER, requiring only 1.41 V relative to the reversible hydrogen electrode (RHE) to drive a current density of 100 mA cm−2 for GOR, and only 0.56 V vs. RHE to achieve the same current density for HER. Moreover, the electrode material still maintains good stability under long-term operation. Among them, the Faraday efficiency (FE) of glycerol oxidation to formate is more than 85 %, while the FE of HER is not less than 93 %.

Surface Ammonium Ions Assisted Decoration of Monodisperse Cobalt Nanoparticles on Molybdenum Oxide Films as Efficient Electrocatalysts for Hydrogen Evolution Reaction.

The high expense associated with electrocatalysts poses a challenge to the advancement of a hydrogen-based energy economy. The utilization of nonprecious metal-based electrocatalysts that are easily prepared and cost-effective is imperative for the future sustainability of a hydrogen society. The semiconductive MoO3-x has been identified as a promising nonprecious electrocatalyst for the hydrogen evolution reaction (HER). Nevertheless, enhancing its relatively low electrocatalytic activity toward HER remains a top priority. This study illustrates the manipulation of surface ammonium ions (NH4+) to produce uniform and distinct cobalt nanoparticles (Co NPs) on active MoO3-x supports, resulting in a more effective heterostructured composite electrocatalyst for HER. The presence of NH4+ ions in the MoO3-x film was extensively examined using infrared spectroscopy, X-ray photoelectron spectroscopy, and UV-visible colorimetric techniques. Additionally, the firmly attached NH4+ ions were employed as binding sites to precipitate Co-containing complex ions. Due to the monolayer-like adsorption of NH4+ ions, only a small quantity of Co precipitate was formed, which was subsequently electrochemically transformed into Co atoms that diffused and created well-separated uniform metallic Co nanoparticles (with an average size of less than 10 nm) on the MoO3-x film. The resulting heterostructure displays a 4.5-fold increase in current density for HER compared to the MoO3-x electrocatalyst through electrochemical assessments. The enhanced catalytic activity was ascribed to the optimized adsorption/desorption of the species involved in water reduction at the heterointerfaces and improved charge transfer rates. These nanoheterostructures hold great promise for a variety of applications in heterogeneous electrocatalysis, while the novel approach could potentially direct the creation of more heterostructures.

Boosting the Hydrogen Evolution Performance of Ultrafine Ruthenium Electrocatalysts by a Hierarchical Phosphide Array Promoter

Tuning the chemical and structural environment of Ru-based nanomaterials is a major challenge for achieving active and stable hydrogen evolution reaction (HER) electrocatalysis. Here, we anchored ultrafine Ru nanoparticles (with a size of ~4.2 nm) on a hierarchical Ni2P array (Ru/Ni2P) to enable highly efficient HER. The Ni2P promoter weakened the adsorption of proton on Ru sites by accepting electrons from Ru nanoparticles. Moreover, the hierarchical Ni2P endowed Ru catalysts with a large surface area and stable open structure. Consequently, the as-fabricated Ru/Ni2P electrode displayed a low overpotential of 57 and 164 mV at the HER current densities of 10 and 50 mA cm−2, respectively, comparable to the state-of-the-art Pt catalysts. Moreover, the Ru/Ni2P electrode can operate stably for 96 h at 50 mA cm−2 without performance degradation. After pairing with a commercial RuO2 anode, the Ru/Ni2P anode catalyzed overall water splitting at 1.73 V with a current density of 10 mA cm−2, which was 0.16 V lower than its commercial Ni counterpart. In situ Raman studies further revealed the optimized proton adsorption at the Ru-active sites on Ni2P promoter, thus enhancing the electrocatalytic HER performance.

The impact of mechanical vibration at cathode on hydrogen yields in water electrolysis

This study investigates the utilization of mechanical vibration to enhance the hydrogen evolution reaction (HER) in electrolysis processes. By varying the force magnitude and frequency of mechanical vibration, significant improvements in HER efficiency were observed. Specifically, the mechanical vibration-assisted electrolysis with a hitting frequency of 3 hits per second and 157.2698 Kg. m−2 hitting force improved the HER current density by 128 % compared to untreated water electrolysis. Linear sweep voltammetry (LSV) data for the graphite electrode revealed a distinct reduction peak at 1 V, indicating a favorable electrochemical reduction reaction influenced by mechanical vibration. The frequency of mechanical vibration significantly impacted the LSV response, with variations in current values across different conditions. Mechanistically, mechanical vibration disrupted intermolecular forces, facilitating better electrode-bubble interactions and accelerating reaction kinetics. Additionally, changes in pH levels induced by mechanical vibration further enhanced HER efficiency. These results suggest that integrating mechanical vibration into electrolysis systems significantly improves HER performance, contributing to the advancement of more efficient and sustainable hydrogen production technologies, which are crucial for achieving net-zero emission targets.

The cobalt-based metal organic frameworks array derived CoFeNi-layered double hydroxides anode and CoP/FeNi2P heterojunction cathode for ampere-level seawater overall splitting

The seawater electrolysis technology powered by renewable energy is recognized as the promising “green hydrogen” production method to solve serious energy and environmental problems. The lack of low-cost and ampere-level current OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) catalysis limits their industrial application. In this work, a unique tri-metal (Co/Fe/Ni) layered double hydroxide hollow array anode catalyst (CFN-LDH/NF) and the CoP/FeNi2P heterojunction hollow array cathode are successfully prepared via one in-situ growth of Co-MOF on nickel foam (Co-MOF/NF) precursor, which exhibits excellent catalytic performance. The η1000 values of 352 and 392 mV are achieved for CFN-LDH/NF (OER catalyst) in 1.0 M KOH and alkaline seawater solution, respectively. The CFNP/NF with a low overpotential of 281 mV is required to reach 1000 mA cm−2 current density for HER in 1.0 M KOH solution, while the η1000 in alkaline seawater solution is 312 mV. The CFN-LDH/NF||CFNP/NF electrolyzer exhibits excellent long-term durability over 100 h, achieving current density of 500 mA cm−2 at 1.825 V in 1.0 M KOH solution. The construction of hollow tri-metal LDH and phosphides heterostructures may open a new and relatively unexplored path for fabricating high performance seawater splitting catalysis.

A highly efficient and self-supporting nanoporous FeMoC catalyst for enhanced hydrogen evolution reaction

Optimizing structure and surface morphologies in electrocatalyst design are important to enhance the intrinsic activity of the hydrogen evolution reaction (HER). Mo-based phosphides and carbides have been confirmed as the widely-reported catalysts for HER. However, the origin of their enhanced catalytic activity is not fully clarified. Herein, the np-FeMoC and np-FeMoP with a self-supporting nanoporous structure were prepared using the melt-spinning and dealloying methods. Benefiting from the self-supporting electrode, nanoporous structure, abundant active species, low charge-transfer resistance and electron synergy, the np-FeMoC exhibits good catalytic performance. The np-FeMoC performs a low overpotential of 50.8 mV at 10 mA cm−2 current density for HER in 1 M KOH. This value is 2.7 times lower than that of the np-FeMoP sample, indicating a synergistic effect between Mo2C and Fe. From XPS and in-situ Raman results, it was observed that the dissolution of Mo2C occurs accompanied by dynamic evolution during the HER process on the np-FeMoC surface. This work unveils the intrinsic activity of Mo-based carbide and phosphide, providing valuable guidance for reasonable exploit of high-performance HER catalysts.

Transient Electro‐Graphitization of MOFs Affecting the Crystallization of Ruthenium Nanoclusters for Highly Efficient Hydrogen Evolution

AbstractFine control over the graphitization level of carbonized nanostructures can play a strategic role in tuning the crystallization of supported nanocatalysts, thereby modulating the kinetics of catalysis. However, realizing the synergistic interplay of graphitization‐tunable support and supported catalysts poses a significant challenge. This study proposes a current pulse‐induced ultrafast strategy for developing MOF‐derived graphitic nano‐leaves (GNL) and supported ultrafine ruthenium nanoclusters exhibiting selective crystallization states depending on the tunable graphitization level of GNL. The resulting ultrafine (≈0.7 nm) amorphous‐ruthenium nanoclusters linked with GNL (a‐Ru@GNL500) exhibit state‐of‐the‐art performance in the hydrogen evolution reaction (HER), requiring very low overpotentials of only 23.0 and 285.0 mV to achieve current densities of 10 and 500 mA cm−2, respectively. Furthermore, a‐Ru@GNL500 demonstrates exceptional operational stability for 100 h under high HER currents of 200 and 400 mA cm−2. Density functional theory reveals that the unique electronic structure of a‐Ru and the cooperative effect of cobalt embedded in the graphitic layer lower the occupancy of the antibonding orbital, resulting in an accelerated HER process. Additionally, the unique electronic structure, highly conducting GNL, and efficient bubble release dynamics of super‐aerophobic a‐Ru@GNL500 contribute to reduced overpotentials, particularly at high HER current densities.

Bimetallic Nitride Ni3Mo3N Microrods with Abundant Catalytic Sites Used as Efficient Electrocatalysts for Hydrogen Evolution Reaction

The importance of efficient and stable hydrogen evolution reaction (HER) electrocatalysts for hydrogen production in alkaline conditions to energy crisis resolution and environmental pollution is immense. In general, the quantity of catalytic sites in the electrocatalyst limits the current density of HER. In response to such problems, the bimetallic effect of non-noble bimetallic nitrides has been shown to regulate the corresponding catalytic sites. Here, a microrod-like non-noble bimetallic nitride catalyst with Ni3Mo3N microrods uniformly modified on nickel foam was synthesized by hydrothermal and nitriding processes. The catalyst showed high catalytic activity for HER in 1 M KOH solution. The overpotential was only 28 mV at a current density of 10 mA·cm−2, demonstrating exceptional electrochemical performance. Furthermore, it exhibited remarkable long-term stability under the same current density. This work will open up a low-cost and simple way for the synthesis of bimetallic nitrides as functional electrode materials for HER and electrochemical detection.

Enriched Se vacancies engineering of RuSe2 induced by low-valence Cu doping for promoting hydrogen evolution and coupling power generation

Heteroatom doping and vacancy engineering play vital roles in designing a high-activity electrocatalyst. Herein, we proposed a novel enriched Se vacancies engineering of the promising ruthenium chalcogenide of RuSe2 induced by low-valence Cu doping for promoting hydrogen evolution reaction (HER) electrocatalysis in alkaline media. The Cu-doped RuSe2 with enriched Se vacancies supported on graphitized carbon (Cu-RuSe2@C) was synthesized by a simple one-step selenization of bimetallic MOF precursor of Ru/Cu-BTC (1,3,5-benzenetricarboxylic acid) polyhedra. Compared to the Cu(Ⅱ)-dominant doped RuSe2 (CuⅡ/Ⅰ-RuSe2@C) with deficient Se vacancies, the proposed Cu(Ⅰ)-dominant doped RuSe2 (CuⅠ/Ⅱ-RuSe2@C) with enriched Se vacancies exhibited significantly improved electrocatalytic activity, which was potentially derived from the created electron-deficient Ruδ+ and Seν− sites induced by low-valence Cu doping. Specifically, CuⅠ/Ⅱ-RuSe2@C needed only 40 mV overpotential to drive a HER current density of 10 mA cm−2, comparable to commercial Pt/C (38 mV) and much lower than those of CuⅡ/Ⅰ-RuSe2@C (93 mV) and RuSe2@C (362 mV). Furthermore, an alkaline Zn-H2O fuel cell with a CuⅠ/Ⅱ-RuSe2@C cathode was integrated to demonstrate its potential applications, which delivered a maximum power density of 15.1 mW cm−2 and specific capacitance of 660 mAh g−1 with good stability. Two series-connected alkaline Zn-H2O cells acted as a chemical energy converter for simultaneous electricity generation and hydrogen coproduction by driving the coupled water splitting.

Engineering of metal Co/Ni-CoO nanoparticles embedded in N-doped unclosed hollow carbon nanoboxes as a highly efficient bifunctional electrocatalyst for overall water splitting

Hollow materials are attracting considerable attention in water electrolysis due to their clear internal space and large surface areas. However, the completely enclosed hollow nanostructures are affected by the large mass-transfer resistance and incompletely exposure of the inner space. Here, an unclosed hollow electrocatalyst consisting of metal Co-loaded Ni-doped CoO multiphase nanoparticles inserted in N-doped hollow carbon shells (Co/Ni-CoO@NC) is designed and constructed by a room-temperature stirring corrosion method and subsequent pyrolysis. The as-prepared Co/Ni-CoO@NC displays outstanding electrocatalytic activities for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolytes. And the optimized products show an ultra-small overpotential of only 61 mV at 10 mA cm−2 current density for HER. For OER, the overpotential is 215 mV at the same current density. The excellent catalytic properties of Co/Ni-CoO@NC are mainly due to the high electrical conductivity of nitrogen-doped carbon materials (NC), the great specific surface area of the hollow NC nanoboxes, the exposed internal space and accessible active sites, and the abundant mass transfer channels of the hollow architectures. Moreover, the obtained catalysts exhibit excellent durability and stability in HER and OER applications. This research develops a feasible way to construct bifunctional unclosed hollow electrocatalysts for decomposing water.

Well-defined Ni3N nanoparticles armored in hollow carbon nanotube shell for high-efficiency bifunctional hydrogen electrocatalysis

Alkaline H2-O2 fuel cells and water electrolysis are crucial for hydrogen energy recycling. However, the sluggish kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) in an alkaline medium pose significant obstacles. Thus, it is imperative but challenging to develop highly efficient and stable non-precious metal electrocatalysts for alkaline HOR and HER. Here, we present the intriguing synthesis of well-defined Ni3N nanoparticles armored within an N-doped hollow carbon nanotube shell (Ni3N@NC) via the conversion of a hydrogen-bonded organic framework (HOF) to metal-organic framework (MOF), followed by high-temperature pyrolysis. As-developed Ni3N@NC demonstrates exceptional bifunctionality in alkaline HOR/HER electrocatalysis, with a high HOR limiting current density of 2.67 mA cm−2 comparable to the benchmark 20 wt% Pt/C, while achieving a lead in overpotential of 145 mV and stronger CO-tolerance. Additionally, it achieves a low overpotential of 21 mV to attain a HER current density of 10 mA cm−2 with long-term stability up to 340 h, both exceeding those of Pt/C. Structural analyses and electrochemical studies reveal that the remarkable bifunctional hydrogen electrocatalytic performance of Ni3N@NC can be ascribed to the synergistic coupling among the well-dispersed small-sized Ni3N nanoparticles, chain-mail structure, and optimized electronic structure enabled by strong metal-support interaction. Furthermore, theoretical calculations indicate that the high-efficiency HOR/HER observed in Ni3N@NC is attributed to the strong OH− affinity, moderate H adsorption, and enhanced water formation/dissociation ability of the Ni3N active sites. This work underscores the significance of rational structural design in enhancing performance and inspires further development of advanced nanostructures for efficient hydrogen electrocatalysis.

High‐Performance Alkaline Freshwater and Seawater Hydrogen Catalysis by Sword‐Head Structured Mo2N‐Ni3Mo3N Tunable Interstitial Compound Electrocatalysts

AbstractRealizing efficient electrocatalysts is a stepping stone toward achieving high‐performance alkaline water/seawater electrolysis, but remains a crucial challenge. Herein, heterogeneous Mo2N/Ni3Mo3N electrocatalysts on nickel foam (denoted MN‐NMN/NF) that is stable and active for the hydrogen evolution reaction (HER) in both alkaline water/seawater are demonstrated. The optimized MN‐NMN09/NF achieves an ultralow HER overpotential of 11 mV@10 mA cm−2 in 1.0 m KOH electrolyte, which is not only superior to the benchmark Pt/C catalysts but also the best reported ever among NiMo‐based electrocatalysts in an alkaline environment. Successively, the optimized MN‐NMN09/NF electrocatalyst can drive HER current densities of 10 and 500 mA cm−2 using low overpotentials of 9.37 and 123 mV in 1.0 m KOH seawater electrolyte, which remains durable after 120 h long‐term electrolysis at a constant current density of 500 mA cm−2. In situ Raman analysis reveals that the enhanced performance is attributed to the accelerated H2O adsorption and OH dissociation processes on the MN‐NMN surfaces. Theoretical analysis further confirms that rapid H2O adsorption‐dissociation kinetics and H adsorption‐conversion kinetics on the Ni3Mo3N/NiOOH and Ni3Mo3N/MoOx surfaces result in boosted HER capability. This work depicts a significant potential for designing stable and efficient hydrogen production electrocatalysts for both alkaline water and seawater electrolysis.

Synthesis of Pure‐Phase Ni2P Nanocatalysts via Phosphorus Ligand Selection for Efficient Hydrogen Evolution Reaction

AbstractDeveloping facile and low‐cost synthetic methods of high‐active platinum group metal‐free electrocatalysts is essential for green hydrogen production primarily based on water electrolysis. We adopted a facile solution‐based synthetic approach to prepare nickel phosphide nanoparticles (NP) and systematically studied the role of phosphorus ligands in the synthesis. Pure‐phase Ni2P NPs were obtained by selecting the proper phosphorus ligands, which tuned the structures of the product. The Ni2P nanowire, prepared using triphenyl phosphite, exhibited the best activity and stability in acidic, neutral, and alkaline media for hydrogen evolution reaction (HER), indicating the advantages of the nanowire structure to the performance. In the acidic medium, it only required overpotential values of 100 and 167 mV to achieve the HER current densities of 10 and 100 mA cm−2, respectively. Furthermore, the overpotential increased only by 26 mV during the 50‐hour stability test, indicating potential for device application. It was also demonstrated that the on‐site generation of insoluble nickel salts (e. g., hydroxides, phosphates, etc.) on the surface resulted in lower activity and stability in neutral and alkaline media than in acid.

Atomically dispersed Ni electrocatalyst for superior urea-assisted water splitting

Urea oxidation reaction (UOR) has been selected as substitution for oxygen evolution reaction ascribing to its low thermodynamic voltage as well as utilization of nickel as electrocatalyst. Herein, we report the formation of nickel single atoms (Ni-SAs) as exceptional bifunctional electrocatalyst toward UOR and hydrogen evolution reaction (HER) in urea-assisted water splitting. In UOR catalysis, Ni-SAs perform a superior catalytic performance than Ni-NP/NC and Pt/C ascribing to the formation of HOO-Ni-N4 structure evidenced by in-situ Raman spectroscopy, corresponding to a boosted mass activity by 175-fold at 1.4 V vs. RHE than Ni-NP/NC. Furthermore, Ni-SAs requires only 450 mV overpotential to obtain HER current density of 500 mA cm−2. 136 mA cm−2 is achieved in urea-assisted water splitting at 1.7 V for Ni-SAs, boosted by 5.7 times than Pt/C-IrO2 driven water splitting.

Interface-induced enhancement of paired electrolysis in 5-hydroxymethylfurfural-H2O system on symbiotic nickel/molybdenum nitride heterostructure

Pairing the hydrogen evolution reaction (HER) with the thermodynamics-friendly electrooxidation reaction (EOR) is a powerful way to maximize the energy/economic effectiveness, but still a challenge. Herein, the symbiotic Ni/MoN heterojunction arrays were constructed on foam (Ni/MoN/NF) by the nitridation-induced in situ reduction/conversion strategy. The fascinating interfacial electronic structure and surface reconstruction of Ni/MoN/NF heterojunction are responsible for the enhanced HMF-H2O paired electrolysis. Ni/MoN/NF only requires a low overpotential of 53 mV to reach the HER current density of 10 mA cm−2, as well as the good durability; and NiOOH derived on the anode are electronically activated by MoN to achieving high-efficiency conversion from HMF to FDCA (∼100 % conversion, 97.5 % yield and 97.4 % Faradaic efficiency). For the HMF-H2O paired electrolysis, the assembled Ni/MoN/NF||Ni/MoN/NF electrolyzer only requires a low potential of 1.391 V to yield the current density of 10 mA cm−2, ranking at the forefront in the reported coupling catalysts. Theoretical calculations manifest that the upshift of d-band center of the NiOOH/MoN heterojunction contributes to HMF chemisorption and activation, thereby enhancing its catalytic activity towards HMFEOR. Our study sheds light on the significance of designing the paired electrolysis with low voltage input for renewable energy applications.

Ru anchored on Co(OH)2 nanowire arrays as highly effective electrocatalyst for full water splitting

With the development of hydrogen energy, it is necessary to develop a cost-effective catalyst for electrochemical water splitting including hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER). Co-based composites are regarded as good catalysts toward OER, but weak H adsorption abilities lead to bad HER activities. Herein, Ru anchored on Co(OH)2 nanowire arrays (Ru/Co(OH)2 NWAs) as bifunctional catalysts for alkaline water splitting, are fabricated by hydrothermal process and subsequent immersion method. Ru/Co(OH)2 NWAs catalyst exhibits excellent activity for HER and OER, owing to strong electronic interaction of Ru participant and Co(OH)2 NWAs. To catalyze 10 mA cm−2 current density for HER and OER, Ru/Co(OH)2 NWAs catalyst only needs the overpotentials of 96 and 186 mV, respectively. An alkali electrolyzer assembled by bifunctional Ru/Co(OH)2 NWAs catalyst delivers 100 mA cm−2 at a cell voltage of 1.76 V, even superior than the couples of Pt/C and RuO2 electrodes (1.88 V).