Efficient Hydrogen Evolution Electrocatalysis Using Cobalt Nanotubes Decorated with Titanium Dioxide Nanodots

Metal-organic frameworks derived carbon-incorporated cobalt/dicobalt phosphide microspheres as Mott-Schottky electrocatalyst for efficient and stable hydrogen evolution reaction in wide-pH environment

Cobalt phosphides, as low cost and abundant non-noble materials for hydrogen evolution reaction (HER), are always constrained by their inferior charge transfer and sluggish intrinsic electrocatalytic kinetics. In this work, carbon-incorporated Co/Co₂P microspheres (Co/Co₂P@C) as a novel Mott-Schottky catalyst were synthesized successfully via carbonization and gradual phosphorization of Co based metal-organic frameworks. The unique merits, including Mott-Schottky effect at the interface formed between metal Co and semiconductor Co₂P, the incorporated carbon-layer on the surface and the spherical structure endow Co/Co₂P@C with favorable electrical conductivity, preferable kinetics and long-term stability when it was evaluated as electrocatalyst for HER in wide-pH range. As a result, the Co/Co₂P@C with the optimized phosphorization degree delivers a benchmark current density of 10 mA cm^-2 at the low overpotential of 192 and 158 mV in acidic and alkaline electrolytes, respectively, with a remarkable stability (CV cycling for 3000 cycles and continuous electrolysis at the overpotential of 200 mV for 48 h). Therefore, the as-designed Co/Co₂P@C should be one of the most promising catalysts for HER application.

First-Principles Mechanistic Insights into the Hydrogen Evolution Reaction on Ni2P Electrocatalyst in Alkaline Medium

Nickel phosphide (Ni2P) is a promising material for the electrocatalytic generation of hydrogen from water. Here, we present a chemical picture of the fundamental mechanism of Volmer–Tafel steps in hydrogen evolution reaction (HER) activity under alkaline conditions at the (0001) and (10 1 ¯ 0) surfaces of Ni2P using dispersion-corrected density functional theory calculations. Two terminations of each surface (Ni3P2- and Ni3P-terminated (0001); and Ni2P- and NiP-terminated (10 1 ¯ 0)), which have been shown to coexist in Ni2P samples depending on the experimental conditions, were studied. Water adsorption on the different terminations of the Ni2P (0001) and (10 1 ¯ 0) surfaces is shown to be exothermic (binding energy in the range of 0.33−0.68 eV) and characterized by negligible charge transfer to/from the catalyst surface (0.01−0.04 e−). High activation energy barriers (0.86−1.53 eV) were predicted for the dissociation of water on each termination of the Ni2P (0001) and (10 1 ¯ 0) surfaces, indicating sluggish kinetics for the initial Volmer step in the hydrogen evolution reaction over a Ni2P catalyst. Based on the predicted Gibbs free energy of hydrogen adsorption (ΔGH*) at different surface sites, we found that the presence of Ni3-hollow sites on the (0001) surface and bridge Ni-Ni sites on the (10 1 ¯ 0) surface bind the H atom too strongly. To achieve facile kinetics for both the Volmer and Heyrovsky–Tafel steps, modification of the surface structure and tuning of the electronic properties through transition metal doping is recommended as an important strategy.

Surface/interface engineering N-doped carbon/NiS2 nanosheets for efficient electrocatalytic H2O splitting

A facile and effective method for preparing bifunctional electrocatalysts with enhanced activity and stability is desired for hydrogen and oxygen production. In this paper, ion-liquid-like (ILL) nickel-urea (Ni-U) was designed and applied to prepare 2D N-doped carbon/NiS₂ (N-C/NiS₂) nanohybrids by a one-step in situ pyrolysis synthesis strategy. The fluidity of ILL Ni-U benefits the interface coupling of the 2D N-C/NiS₂ nanohybrid. Due to the synergistic effect between NiS₂ and N-carbon with high conductivity, the H₂O splitting performance of 2D N-C/NiS₂ nanohybrids was significantly enhanced in alkaline media. The corresponding two-electrode cell only needed 1.53 V to undertake 10 mA cm^-2 for H₂O splitting. Moreover, the resultant 2D N-C/NiS₂ nanohybrids exhibited lasting electrochemical endurance with the maintenance of its stability for more than 48 h. The synthetic strategy not only provides a simple and scalable route for constructing 2D hybrid electrocatalysts, but also paves a way to improve the HER/OER activity of sulphides via the surface/interface engineering strategy.

A novel MoNi@Ni(OH)2 heterostructure with Pt-like and stable electrocatalytic activity for the hydrogen evolution reaction

A novel Mo0.84Ni0.16@Ni(OH)2 heterostructure was successfully fabricated. Owing to the unique interface structure and strong synergistic effects between different components, the heterostructure shows enhanced activity for the hydrogen evolution reaction (HER), outperforming that of the state-of-the-art Pt/C catalyst.

Enhancement of HER kinetics with RhNiFe for high-rate water electrolysis

The NiFeCHH is best for OER and poor for HER which by introducing Rh, showed total water splitting in KOH. It requires an ultra-low overpotential of just 36 mV at 50 mA cm⁻² for HERs and 286 mV at 50 mA cm⁻² for TWS.

Metal–organic framework derived nitrogen-doped carbon-RhNi alloys anchored on graphene for highly efficient hydrogen evolution reaction

Nitrogen-doped carbon-RhNi alloy nanoparticles anchored on reduced graphene oxide nanosheet hybrid structure (NC-RhNi/rGO) exhibit high HER performance.

Cation-Modulated HER and OER Activities of Hierarchical VOOH Hollow Architectures for High-Efficiency and Stable Overall Water Splitting

Atom-scale modulation of electronic regulation in nonprecious-based electrocatalysts is promising for efficient catalytic activities. Here, hierarchically hollow VOOH nanostructures are rationally constructed by partial iron substitution and systematically investigated for electrocatalytic water splitting. Benefiting from the hierarchically stable scaffold configuration, highly electrochemically active surface area, the synergistic effect of the active metal atoms, and optimal adsorption energies, the 3% Fe (mole ratio) substituted electrocatalyst (VOOH-3Fe) exhibits a low overpotential of 90 and 195 mV at 10 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media, respectively, superior than the other samples with a different substituted ratio. To the best of current knowledge, 195 mV overpotential at 10 mA cm^-2 is the best value reported for V or Fe (oxy)hydroxide-based OER catalysts. Moreover, the electrolytic cell employing the VOOH-3Fe electrode as both the cathode and anode exhibits a cell voltage of 0.30 V at 10 mA cm^-2 with a remarkable stability over 60 h. This work heralds a new pathway to design efficient bifunctional catalysts toward overall water splitting.

Hydrogen Evolution Enhancement over a Cobalt-Based Schottky Interface

A proof-of-concept strategy for significant enhancement of hydrogen evolution reaction (HER) performance of transition metals via construction of a metal/semiconductor Schottky junction is presented. The decoration of low-cost commercial TiO₂ nanoparticles on the surface of microscale Co dendrites causes a significant charge transfer across the Co/TiO₂ Schottky interface and enhances the local electron density at the Co surface, confirmed by X-ray photoelectron spectroscopy results and density functional theory calculations. The Co/TiO₂ Schottky catalyst displays superior HER activity with a turnover frequency of 0.052 s^-1 and an exchange current density of 79 μA cm^-2, which are about 4.3 and 4.0 times greater than that of pristine Co, respectively. Moreover, the Co/TiO₂ Schottky catalyst displays excellent electrochemical durability for long-term operation in both alkaline solution and high saline solution. Theoretical calculations suggest that the Schottky junction plays an important role to optimize hydrogen adsorption free energy (ΔG_H*) by tuning the electronic structure, which enhances the performance for HER of the Co/TiO₂ Schottky catalyst. This study of modulating the electronic structure of the catalysts via the Schottky junction could provide valuable insights for designing and synthesizing low-cost, high-performance electrocatalysts.

In Situ Growth of Ag Nanodots Decorated Cu2 O Porous Nanobelts Networks on Copper Foam for Efficient HER Electrocatalysis

Developing earth-abundant electrocatalysts for high-efficiency hydrogen evolution reaction (HER) has become one of the leading research frontiers in energy conversion. Here, the design and in situ growth of Ag nanodots decorated Cu₂ O porous nanobelts networks on Cu foam (denoted as Ag@Cu₂ O/CF) are carried out via a simple one-pot solution strategy at room temperature. Serving as self-supporting electrocatalysts, Ag@Cu₂ O porous nanobelts provide plentiful active sites, and the 3D hybrid foams provide fast transportation for electrolyte and short diffusion path for newly formed H₂ bubbles, which result in excellent electrocatalytic HER activity and long-term stability. Owing to the synergistic effect between Ag nanodots and Cu₂ O porous nanobelts and CF, the hybrid electrocatalyst exhibits a low Tafel slope of 58 mV dec^-1 , a small overpotential of 108 mV at 10 mA cm^-2 , and high durability for more than 20 h at a potential of 200 mV for HER in 1.0 mol L^-1 KOH solution.

Engineering MoS2 Basal Planes for Hydrogen Evolution via Synergistic Ruthenium Doping and Nanocarbon Hybridization

Promoting the intrinsic activity and accessibility of basal plane sites in 2D layered metal dichalcogenides is desirable to optimize their catalytic performance for energy conversion and storage. Herein, a core/shell structured hybrid catalyst, which features few-layered ruthenium (Ru)-doped molybdenum disulfide (MoS2) nanosheets closely sheathing around multiwalled carbon nanotube (CNT), for highly efficient hydrogen evolution reaction (HER) is reported. With 5 at% (atomic percent) Ru substituting for Mo in MoS2, Ru-MoS2/CNT achieves the optimum HER activity, which displays a small overpotential of 50 mV at -10 mA cm-2 and a low Tafel slope of 62 mV dec-1 in 1 m KOH. Theoretical simulations reveal that Ru substituting for Mo in coordination with six S atoms is thermodynamically stable, and the in-plane S atoms neighboring Ru dopants represent new active centers for facilitating water adsorption, dissociation, and hydrogen adsorption/desorption. This work provides a multiscale structural and electronic engineering strategy for synergistically enhancing the HER activity of transition metal dichalcogenides.

Cu3N nanowire array as a high-efficiency and durable electrocatalyst for oxygen evolution reaction

Developing non-precious oxygen evolution reaction (OER) electrocatalysts with high performance and long-term stability has drawn considerable research interest in recent years. In this communication, we report a self-supported Cu3N nanowire array on copper foam (Cu3N NA/CF) which is derived from a Cu(OH)2 nanowire array on copper foam (Cu(OH)2 NA/CF) through a nitridation process. Intriguingly, this 3D electrode exhibits marvellous OER activity with the need of an overpotential of only 298 mV at a current density of 20 mA cm-2 in 1.0 M KOH. In addition, the obtained electrocatalyst is capable of maintaining its high performance for at least 25 h under a static current density of 20 mA cm-2.

Nitrogen-plasma treated hafnium oxyhydroxide as an efficient acid-stable electrocatalyst for hydrogen evolution and oxidation reactions

Development of earth-abundant electrocatalysts for hydrogen evolution and oxidation reactions in strong acids represents a great challenge for developing high efficiency, durable, and cost effective electrolyzers and fuel cells. We report herein that hafnium oxyhydroxide with incorporated nitrogen by treatment using an atmospheric nitrogen plasma demonstrates high catalytic activity and stability for both hydrogen evolution and oxidation reactions in strong acidic media using earth-abundant materials. The observed properties are especially important for unitized regenerative fuel cells using polymer electrolyte membranes. Our results indicate that nitrogen-modified hafnium oxyhydroxide could be a true alternative for platinum as an active and stable electrocatalyst, and furthermore that nitrogen plasma treatment may be useful in activating other non-conductive materials to form new active electrocatalysts.

Renewable hydrogen technologies are promising for alternative energy, but are encumbered by the kinetics of electrochemical reactions in harsh conditions. Here, authors report nitrogen-modified hafnium oxyhydroxide for electrocatalysis of hydrogen evolution and oxidation reactions in acidic media.

Flexible vanadium-doped Ni2P nanosheet arrays grown on carbon cloth for an efficient hydrogen evolution reaction

Tuning the electronic structure, morphology, and structure of electrocatalysts is of great significance to achieve a highly active and stable hydrogen evolution reaction (HER). Herein, combining hydrothermal and low temperature phosphidation methods, V-doped Ni2P nanosheet arrays grown on carbon cloth (V-Ni2P NSAs/CC) were successfully prepared for the HER. It is found that the prepared V-Ni2P NSAs/CC exhibits preeminent performance for the HER. Specifically, it only requires an overpotential of 85 mV to achieve a current density of 10 mA cm-2 in 1.0 M KOH solution. Moreover, the V-Ni2P NSAs/CC shows superior electrochemical stability, maintaining its HER performance up to 3000 cyclic voltammetry cycles. This work affords a guiding strategy for the synthesis of a high-performance and stable electrocatalyst for the HER.

One-dimensional CoS2-MoS2 nano-flakes decorated MoO2 sub-micro-wires for synergistically enhanced hydrogen evolution

CoS2-MoS2 nanoflakes decorated MoO2 (CoMoOS) hybrid submicro-wires with rich active interfaces were synthesized via the sulfuration of CoMoO4. They showed excellent activity while synergistically catalyzing the hydrogen evolultion reaction (HER) in basic media by promoting both the water dissociation and hydrogen absorption steps. Thus, the CoMoOS catalysts only needed 123 mV to achieve 10 mA cm-2 with a small Tafel slope in alkaline solutions, and required 1.68 V to obtain the same current density when assembled into an alkaline electrolyser.

Efficient Hydrogen Evolution Activity and Overall Water Splitting of Metallic Co4N Nanowires through Tunable d-Orbitals with Ultrafast Incorporation of FeOOH

Cobalt nitride electrocatalysts have been investigated and proven to show excellent oxygen evolution reaction activity owing to their excellent metallic properties, but their hydrogen evolution reaction (HER) properties are rarely reported because of their unsatisfactory molecular energy level, especially the d-orbital. Herein, taking Co₄N as a case study, we tune the d-orbital of metallic Co₄N nanowires via rapid formation of iron oxyhydroxide (FeOOH). Experimental analyses show that FeOOH@Co₄N/SSM exhibits excellent HER catalytic activity with considerable low onset overpotential (22 mV), small Tafel slope (34 mV dec^-1), and excellent stability at current densities ranging from 20 to 100 mA cm^-2. Additionally, theoretical assessments display that the hybridization of Co₄N with FeOOH is beneficiary for optimizing and promoting the free energy of H adsorption due to the tuning of d-orbital. An overall water-splitting device assembled based on bifunctional FeOOH@Co₄N/SSM delivers an onset potential of 1.48 V with excellent stability up to 4 days. This shows a new strategy for designing a high-performance water-splitting device based on cobalt-based electrocatalysts.

Heterostructures Composed of N-Doped Carbon Nanotubes Encapsulating Cobalt and β-Mo2 C Nanoparticles as Bifunctional Electrodes for Water Splitting

Herein, we demonstrate the use of heterostructures comprised of Co/β-Mo₂ C@N-CNT hybrids for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline electrolyte. The Co can not only create a well-defined heterointerface with β-Mo₂ C but also overcomes the poor OER activity of β-Mo₂ C, thus leading to enhanced electrocatalytic activity for HER and OER. DFT calculations further proved that cooperation between the N-CNTs, Co, and β-Mo₂ C results in lower energy barriers of intermediates and thus greatly enhances the HER and OER performance. This study not only provides a simple strategy for the construction of heterostructures with nonprecious metals, but also provides in-depth insight into the HER and OER mechanism in alkaline solution.

Research Advances of Amorphous Metal Oxides in Electrochemical Energy Storage and Conversion

Amorphous metal oxides (AMOs) have aroused great enthusiasm across multiple energy areas over recent years due to their unique properties, such as the intrinsic isotropy, versatility in compositions, absence of grain boundaries, defect distribution, flexible nature, etc. Here, the materials engineering of AMOs is systematically reviewed in different electrochemical applications and recent advances in understanding and developing AMO-based high-performance electrodes are highlighted. Attention is focused on the important roles that AMOs play in various energy storage and conversion technologies, such as active materials in metal-ion batteries and supercapacitors as well as active catalysts in water splitting, metal-air batteries, and fuel cells. The improvements of electrochemical performance in metal-ion batteries and supercapacitors are reviewed regarding the enhancement in active sites, mechanical strength, and defect distribution of amorphous structures. Furthermore, the high electrochemical activities boosted by AMOs in various fundamental reactions are elaborated on and they are related to the electrocatalytic behaviors in water splitting, metal-air batteries, and fuel cells. The applications in electrochromism and high-conducting sensors are also briefly discussed. Finally, perspectives on the existing challenges of AMOs for electrochemical applications are proposed, together with several promising future research directions.

Efficient oxygen evolution on mesoporous IrOx nanosheets

Amorphous iridium oxide (IrO_x) is a promising catalyst that has high activity in the oxygen evolution reaction (OER) over a broad range of pH values.

Strongly Coupled Nickel-Cobalt Nitrides/Carbon Hybrid Nanocages with Pt-Like Activity for Hydrogen Evolution Catalysis

Designing non-precious-metal catalysts with comparable mass activity to state-of-the-art noble-metal catalysts for the hydrogen evolution reaction (HER) in alkaline solution still remains a significant challenge. Herein a new strongly coupled nickel-cobalt nitrides/carbon complex nanocage (NiCoNzocage) is rationally designed via chemical etching of ZIF-67 nanocubes with Ni(NO₃ )₂ under sonication at room temperature, following nitridation. The as-prepared strongly coupled NiCoN/C nanocages exhibit a mass activity of 0.204 mA µg^-1 at an overpotential of 200 mV for the HER in alkaline solution, which is comparable to that of commercial Pt/C (0.451 mA µg^-1 ). The strongly coupled NiCoN/C nanocages also possess superior stability for the HER with negligible current loss under the overpotentials of 200 mV for 10 h. Density functional theory (DFT) calculations reveal that the excellent HER performance under alkaline condition arises from the robust Co²⁺ →Co⁰ transformation achieved by strong (Ni, Co)N-bonding-induced efficient d-p-d coupled electron transfer, which is a key for optimal initial water adsorption and splitting. The high degree of amorphization urges the C-sites to be an electron-pushing bath to promote the inter-layer/sites electron-transfer with loss of the orbital-selection-forbidden-rule, which uniformly boosts the surface catalytic activities up to a high level independent of the individual surface active sites.

In situ formed oxy/hydroxide antennas accelerating the water dissociation kinetics on a Co@N-doped carbon core–shell assembly for hydrogen production in alkaline solution

The hydrogen evolution reaction (HER) in alkaline electrolytes is restricted severely by sluggish water dissociation in the Volmer step.

Combining High Porosity with High Surface Area in Flexible Interconnected Nanowire Meshes for Hydrogen Generation and Beyond

Nanostructured metals with large surface area have a great potential for multiple device applications. Although various metal architectures based on metal nanoligaments and nanowires are well known, they typically show a tradeoff between mechanical robustness, high surface area, and high (macro)porosity, which, when combined, could significantly improve the performance of devices such as batteries, electrolyzers, or sensors. In this work, we rationally designed templated networks of interconnected metal nanowires, combining for the first time high porosity of metal foams, narrowly distributed macropores, and a very high surface area of nanoporous dealloyed metals. Thanks to their structural uniformity, the few-micron thick nanowire meshes are also remarkably flexible and durable. We show how the textural properties of the material can be precisely tuned to optimize the nanowire networks for applications in different devices. In an exemplary application in electrolytic production of hydrogen, thanks to its high surface area, a few-micron thick nanomesh outperformed a 300 times thicker nickel foam. Furthermore, thanks to its high porosity, the Pt-doped nanomesh surpassed a microporous Pt/C cloth, demonstrating benefits of the optimally designed nanowire structure for a simultaneous improvement and miniaturization of electrochemical devices. This work extends the potential of interconnected nanowires to multiple new research and industrial applications requiring highly porous and flexible conductive materials with a high surface-to-volume ratio.

Recent progress in transition metal phosphides with enhanced electrocatalysis for hydrogen evolution

Increasing demand for hydrogen energy has boosted the exploration of inexpensive and effective catalysts. Transition metal phosphides (TMPs) have been proven as excellent catalysts for the hydrogen evolution reaction (HER). Very recently, the search for TMP-based catalysts has being mainly directed at enhanced electrocatalytic performance. Hence, a concluded guideline for enhancing HER activity is highly desired. In this mini review, we briefly summarize the most recent and instructive developments in the design of TMP-based catalysts with enhanced electrocatalysis for hydrogen evolution from composition and structure engineering strategies. These strategies and perspectives are also meaningful for designing other inexpensive and high-performance catalysts.

CuO/Co(OH)2 Nanosheets: A Novel Kind of Electrocatalyst for Highly Efficient Electrochemical Oxidation of Methanol

With the booming of non-noble-metal electrocatalysts for efficient oxygen reduction reaction under alkaline conditions, corresponding anodic catalysts for methanol oxidation are urgently needed especially for direct methanol fuel cells with alkaline membranes. Here, we report the facile synthesis of a CuO/Co(OH)₂-nanosheet composite as a novel kind of high-performance electrochemical methanol oxidation reaction (MOR) catalyst. The obtained material with an optimized Cu/Co ratio shows much enhanced mass activity and area-specific activity, as well as excellent stability. The electronic structure interaction between Cu and Co, which results in the Co ion binding-energy elevation, is considered to be the origin of high MOR performance. This work promises the great potential of cobalt hydroxide as a novel kind of MOR catalyst and may arouse much interest in exploring more hydroxides as efficient nonprecious-metal electrocatalysts for MOR.

Mechanochemically Assisted Synthesis of a Ru Catalyst for Hydrogen Evolution with Performance Superior to Pt in Both Acidic and Alkaline Media

Catalysts are at the heart of the hydrogen evolution reaction (HER) for the production of pure and clean hydrogen. For practical applications, the scalable synthesis of efficient HER catalysts, which work in both acidic and alkaline media, is highly desired. In this work, the mechanochemically assisted synthesis of a Ru catalyst with HER performance surpassing Pt in both acidic and alkaline media is reported. Mass production of this Ru catalyst can be achieved via a two-step procedure: the mechanochemical reaction between graphite and dry ice produces edge-carboxylic-acid-functionalized graphene nanoplatelets (CGnP); mixing a Ru precursor and the CGnP in an aqueous medium introduces Ru ions, which coordinate on the CGnP. Subsequent annealing results in uniform Ru nanoparticles (≈2 nm) anchored on the GnP matrix (Ru@GnP). The efficient Ru@GnP catalyst can be easily powered by a single silicon solar cell using a wireless integration device. The self-powered device exhibits robust hydrogen evolution under the irradiation of standard AM 1.5 solar light. This work provides a new opportunity for the low-cost mass production of efficient and stable catalysts for practical applications.

One-step electrodeposition of a hierarchically structured S-doped NiCo film as a highly-efficient electrocatalyst for the hydrogen evolution reaction

An enormous challenge in the development of renewable hydrogen sources for electricity-driven water-splitting systems has been the limitation of the earth-abundant and robust highly-active cathode electrocatalysts. In this work, we developed a simple sulfur-anion doping strategy to obtain the S-doped NiCo composite (S-NiCo@50) on Ni foam (NF) via a one-step electrochemical deposition. It was found that doped sulfur plays a crucial role in reducing the overpotential of hydrogen evolution by providing abundant active sites as identified by the XPS spectrum. The formed metallic Ni and Co effectively promoted electron transportation. The synergistic effects between the amorphous CoxNiyS(x+y) substance and crystalline Ni and Co metal seemed to result in enhanced HER activity. In particular, the S-NiCo@50 electrode, featuring a hierarchical morphology, showed an ultralow overpotential of 28 and 125 mV at 10 and 100 mA cm-2, respectively, in 1.0 M NaOH with a large exchange current density (j0) of 4.8 mA cm-2 as well as high conductivity and stability; its catalytic properties are superior to most of the reported alkaline electrocatalysts and are on par with commercial Pt/C. Assembled with the counter electrode (Ni-Fe/NF), the overall water splitting was proved with a low 1.55 V at 10 mA cm-2. Moreover, we built the Ni24Co6S6 cluster as the S-NiCo@50 model and revealed its intrinsic activity by density functional theory (DFT) calculations. This study shows that S-doping and component control can be an exquisite strategy for realizing high-efficiency electrochemical water reduction.

High-Efficient, Stable Electrocatalytic Hydrogen Evolution in Acid Media by Amorphous Fex P Coating Fe2 N Supported on Reduced Graphene Oxide

Development of efficient and durable non-Pt catalysts for hydrogen evolution reaction (HER) in acid media is highly desirable. Iron nitride has emerged as a promising catalyst for its cost-effective nature, but the corresponding acidic stability must be promoted. Herein, phosphorus-decorated Fe₂ N and reduced graphene oxide (P-Fe₂ N/rGO) composite are designed and synthesized. X-ray photoelectron spectroscopy and X-ray absorption fine structure (XAFS) show that a thin layer amorphous iron phosphide is coated on the surface of Fe₂ N nanoparticles, which could be responsible for the well resistance of chemical corrosion in acidic media. Meanwhile, the P-decoration could tune the electronic state and coordination environment of iron atom as evidenced by XAFS, resulting in dramatically enhanced electrocatalytic activity of P-Fe₂ N/rGO. Density functional theory calculations reveal that both the P-connected N atoms and the Fe atoms in P-Fe₂ N/rGO catalyst are the main active sites for H* adsorption. The hydrogen-binding free energy |ΔG_H* | value is close to zero for P-Fe₂ N/rGO, suggesting a good balance between the Volmer and Heyrovsky/Tafel steps in HER kinetics. As expected, P-Fe₂ N/rGO catalyst could achieve a low η_onset of 22.4 mV, a small Tafel plot of 48.7 mV dec^-1 , and remarkable stability for HER in acid electrolyte.

Solution-Plasma-Assisted Bimetallic Oxide Alloy Nanoparticles of Pt and Pd Embedded within Two-Dimensional Ti3C2T x Nanosheets as Highly Active Electrocatalysts for Overall Water Splitting

Exploiting high-efficiency and low-cost bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been actively encouraged because of their potential applications in the field of clean energy. In this paper, we reported a novel electrocatalyst based on an exfoliated two-dimensional (2D) MXene (Ti₃C₂T _x) loaded with bimetallic oxide alloy nanoparticles (NPs) of Pt and Pd (represented by PtO _aPdO _bNPs@Ti₃C₂T _x), which was synthesized via solution plasma (SP) modification. The prepared materials were then utilized as highly efficient bifunctional electrocatalysts toward the HER and OER in alkaline solution. At a high plasma input power (200 W), bimetallic oxide alloy nanoparticles of Pt and Pd or nanoclusters with different metallic valence states were deposited onto the Ti₃C₂T _x nanosheets. Because of the synergism of the noble-metal NPs and the Ti₃C₂T _x nanosheets, the electrocatalytic results revealed that the as-prepared PtO _aPdO _bNPs@Ti₃C₂T _x nanosheets under the plasma input power of 200 W for 3 min only required a low overpotential to attain 10 mA cm^-2 for the HER (-26.5 mV) in 0.5 M H₂SO₄ solution and OER (1.54 V) in 0.1 M KOH solution. Moreover, water electrolysis using this catalyst achieved a water splitting current density of 10 mA cm^-2 at a low cell voltage of 1.53 V in 1.0 M KOH solution. These results suggested that the hybridization of the extremely low usage of PtO _a/PdO _b NPs (1.07 μg cm^-2) and Ti₃C₂T _x nanosheets by SP will expand the applications of other clean energy reactions to achieve sustainable energy.

Transition Metal Induced the Contraction of Tungsten Carbide Lattice as Superior Hydrogen Evolution Reaction Catalyst

Tungsten carbide (WC) materials have exhibited platinum-like catalytic behavior in many fields, whereas the adsorption of pure tungsten carbide for H is too strong and demonstrates low activity for hydrogen evolution reaction (HER). Herein, we successfully introduced transition metal into WC lattice and optimized the electron structure around Fermi level ( E_F) of WC via facile annealing CoW-based metal-organic framework precursors. X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption fine structure verified the incorporation of Co and the contraction of WC lattice. Density functional theory calculations indicated that the doping of Co into WC significantly increases the state density of WC at E_F derived from the delocalization of Co charge, resulting in the moderate H₂O binding energy and weakened H adsorption. As expected, the optimal Co-doping WC (Co/W molar ratio = 3) efficiently catalyzed HER with a low onset potential (31 mV) and a current density of 10 mA cm^-2 at a low overpotential of 98 mV in 1.0 M KOH media, which was superior to that of WC/CN and Co/CN. Similarly, Ni and Fe could also modulate the electronic structure of WC and improve the HER activity.

CoSe2 /MoSe2 Heterostructures with Enriched Water Adsorption/Dissociation Sites towards Enhanced Alkaline Hydrogen Evolution Reaction

Transition-metal dichalcogenides (TMDs) are promising electrocatalysts toward the hydrogen evolution reaction (HER) in acid media, but they show significantly inferior activity in alkaline media due to the extremely sluggish water dissociation kinetics. Herein, CoSe₂ /MoSe₂ heterostructures with CoSe₂ quantum dots anchored on MoSe₂ nanosheets are synthesized towards enhanced alkaline HER catalytic activity. The incorporation of CoSe₂ is intended to construct additional water adsorption sites on the basal planes of MoSe₂ to promote water dissociation. The CoSe₂ /MoSe₂ heterostructures show substantially enhanced activity over MoSe₂ and CoSe₂ in 1 m KOH. The optimal overpotential required to reach a current density of 10 mA cm^-2 is merely 218 mV, which is more than 100 mV greater than that of MoSe₂ , which is by far the best performance demonstrated for precious-metal-free catalysts. Detailed analyses based on electrochemical testing demonstrate that the water adsorption and subsequent dissociation process is accelerated by CoSe₂ species with rich edge sites; meanwhile, MoSe₂ species provide sufficient active sites for the adsorption and combination of adsorbed hydrogen (H^. ). These results provide an effective strategy for developing earth-abundant catalysts with high activity for the alkaline HER, and are of great significance to promote the practical application of alkaline water electrolysis.

TePtFe Nanotubes as High-Performing Bifunctional Electrocatalysts for the Oxygen Reduction Reaction and Hydrogen Evolution Reaction

Currently, a multicomponent platinum-based alloy has been applied as a promising electrocatalyst to improve catalysis and lower the usage of the noble metal platinum. Herein, a tellurium nanowire (NW)-derived ternary TePtFe nanotube (NT) electrocatalyst has been prepared by the Kirkendall effect. The TePtFe NT formed consists of small single-crystal nanoparticles and voids with an open-end and hollow structure. The TePtFe NT electrocatalyst presents an impressive catalytic activity and stability for both the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Its ORR specific activity and mass activity are 8.5 and 2.4 times, respectively, improved relative to those of commercial platinum catalysts. It is also impressive that, for the HER, a very low overpotential of 28.1 mV at 10 mA cm^-2 can be achieved; this is lower than that of platinum (51.8 mV) catalysts in 0.1 m HClO₄ , and the activity is improved, even after 5000 cycles. This work reveals that TePtFe NTs can be employed as nanocatalysts with an impressive catalytic activity and stability for application in fuel cells and hydrogen production.

Spatially Confined Assembly of Monodisperse Ruthenium Nanoclusters in a Hierarchically Ordered Carbon Electrode for Efficient Hydrogen Evolution

The redox units of polyaniline (PAni) are used cooperatively, and in situ, to assemble ruthenium (Ru) nanoclusters in a hierarchically ordered carbon electrode. The oxidized quinonoid imine (QI) units in PAni bond Ru complex ions selectively, whereas reduced benzenoid amine (BA) units cannot. By electrochemically tuning the ratio of QI to BA, Ru complexes are spatially confined in the outer layer of hierarchical PAni frameworks. Carbonization of Ru-PAni hybrids induces nucleation on the outer surface of the carbon support, generating nearly monodisperse Ru nanoclusters. The optimized catalyst has a low loading of approximately 2 wt % Ru, but exhibits a mass activity for the hydrogen evolution reaction that is about 6.8 times better than commercial 20 wt % Pt/C catalyst.