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

Innovative Electrochemical Strategies for Hydrogen Production: From Electricity Input to Electricity Output

Renewable H₂ production by water electrolysis has attracted much attention due to its numerous advantages. However, the energy consumption of conventional water electrolysis is high and mainly driven by the kinetically inert anodic oxygen evolution reaction. An alternative approach is the coupling of different half-cell reactions and the use of redox mediators. In this review, we, therefore, summarize the latest findings on innovative electrochemical strategies for H₂ production. First, we address redox mediators utilized in water splitting, including soluble and insoluble species, and the corresponding cell concepts. Second, we discuss alternative anodic reactions involving organic and inorganic chemical transformations. Then, electrochemical H₂ production at both the cathode and anode, or even H₂ production together with electricity generation, is presented. Finally, the remaining challenges and prospects for the future development of this research field are highlighted.

Homogenous Cr and C Doped 3D Self-Supporting NiO Cellular Nanospheres for Hydrogen Evolution Reaction

Hydrogen evolution reaction (HER) is one promising technique to obtain high-purity hydrogen, therefore, exploiting inexpensive and high-efficiency HER electrocatalysts is a matter of cardinal significance under the background of achieving carbon neutrality. In this paper, a hydrothermal method was used to prepare the Cr-NiC₂O₄/NF (Ni foam) precursor. Then, the NiO-Cr-C/NF self-supporting HER catalyst was obtained by heating the precursor at 400 °C. The catalyst presents a 3D cellular nanospheres structure which was composed of 2D nanosheets. Microstructure characterization shows that Cr and C elements were successfully doped into NiO. The results of electrochemical measurements and density functional theory (DFT) calculations show that under the synergy of Cr and C, the conductivity of NiO was improved, and the Gibbs free energy of H* (∆GH*) value is optimized. As a result, in 1.0 M KOH solution the NiO-Cr-C/NF-3 (Ni:Cr = 7:3) HER catalyst exhibits an overpotential of 69 mV and a Tafel slope of 45 mV/dec when the current density is 10 mA·cm^-2. Besides, after 20 h of chronopotentiometry, the catalytic activity is basically unchanged. It is demonstrated that C and Cr co-doping on the lattice of NiO prepared by a simple hydrothermal method and subsequent heat treatment to improve the catalytic activity and stability of the non-precious metal HER catalysts in an alkaline medium is facile and efficient.

Unlocking Interfacial Electron Transfer of Ruthenium Phosphides by Homologous Core-Shell Design toward Efficient Hydrogen Evolution and Oxidation

Developing high-efficiency electrocatalysts for the hydrogen evolution and oxidation reactions (HER/HOR) in alkaline electrolytes is of critical importance for realizing renewable hydrogen technologies. Ruthenium phosphides (RuP_x ) are promising candidates to substitute Pt-based electrodes; however, great challenges still remain in their electronic structure regulation for optimizing intermediate adsorption. Herein, it is reported that a homologous RuP@RuP₂ core-shell architecture constructed by a phosphatization-controlled phase-transformation strategy enables strong electron coupling for optimal intermediate adsorption by virtue of the emergent interfacial functionality. Density functional theory calculations show that the RuP core and RuP₂ shell present efficient electron transfer, leading to a close to thermoneutral hydrogen adsorption Gibbs free energy of 0.04 eV. Impressively, the resulting material exhibits superior HER/HOR activities in alkaline media, which outperform the benchmark Pt/C and are among the best reported bifunctional hydrogen electrocatalysts. The present work not only provides an efficient and cost-effective bifunctional hydrogen electrocatalyst, but also offers a new synthetic protocol to rationally synthesize homologous core-shell nanostructures for widespread applications.

Vacancy-Rich MXene-Immobilized Ni Single Atoms as a High-Performance Electrocatalyst for the Hydrazine Oxidation Reaction

Single-atom catalysts (SACs), on account of their outstanding catalytic potential, are currently emerging as high-performance materials in the field of heterogeneous catalysis. Constructing a strong interaction between the single atom and its supporting matrix plays a pivotal role. Herein, Ti₃ C₂ T_x -MXene-supported Ni SACs are reported by using a self-reduction strategy via the assistance of rich Ti vacancies on the Ti₃ C₂ T_x MXene surface, which act as the trap and anchor sites for individual Ni atoms. The constructed Ni SACs supported by the Ti₃ C₂ T_x MXene (Ni SACs/Ti₃ C₂ T_x ) show an ultralow onset potential of -0.03 V (vs reversible hydrogen electrode (RHE)) and an exceptional operational stability toward the hydrazine oxidation reaction (HzOR). Density functional theory calculations suggest a strong coupling of the Ni single atoms and their surrounding C atoms, which optimizes the electronic density of states, increasing the adsorption energy and decreasing the reaction activation energy, thus boosting the electrochemical activity. The results presented here will encourage a wider pursuit of 2D-materials-supported SACs designed by a vacancy-trapping strategy.

Nitrogen-doped Ru film for energy-saving hydrogen production assisted with hydrazine oxidation

Herein, a universal approach is proposed to prepare a nitrogen-doped mesoporous Ru film with uniform pore size on nickel foam (N-mRu/NF) as an active bifunctional catalyst for energy-saving hydrogen production. The N-mRu/NF requires an ultrasmall overpotential of -60 and 62 mV to achieve 100 mA cm^-2 for the hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), respectively. When used for HER-HzOR electrolysis, N-mRu/NF requires low voltages of 0.023 and 0.184 V at 10 and 100 mA cm^-2, respectively.

Electronegativity Enhanced Strong Metal-Support Interaction in Ru@F-Ni3N for Enhanced Alkaline Hydrogen Evolution

Precious metals (Pt, Ir, Ru, and so on) and related compounds usually demonstrate superb catalytic activity for electrochemical hydrogen production. However, scarcity and stability are still challenges for hydrogen evolution reaction, even for single-atomic-site electrocatalysts. Herein, a fluorine (F) doping strategy is proposed to enhance the strong metal-support interaction between the F-doped Ni₃N support and the loaded ruthenium (Ru) species. Via synergistically modulating both the Ru loading amount and F doping concentration, outstanding HER activity was achieved in Ru@F-Ni₃N with an overpotential (η) of 115 mV at 100 mA cm^-2, superior to the benchmark Pt/C (η = 201 mV). Density functional theory simulation in combination with X-ray photoelectron spectra and X-ray absorption spectroscopy characterizations convincingly demonstrate that, with the strongest electronegativity, F doping could effectively stabilize Ru atoms doped in the F-Ni₃N substrate and simultaneously reduce the H bonding strength, which accelerated the desorption of H₂. These findings provide a facile strategy to modulate both catalytic activities and stabilities of heteroatom-loaded catalytic materials.

Hydrogen Production and Water Desalination with On-demand Electricity Output Enabled by Electrochemical Neutralization Chemistry

Energy-saving hydrogen production can be achieved by using renewables or decoupling the sluggish oxygen evolution reaction from overall water splitting, which still needs electricity input. We have realized hydrogen production and water desalination with on-demand electricity output via an electrochemical neutralization chemistry strategy that couples acidic hydrogen evolution and alkaline hydrazine oxidation with ionic exchange. The electrochemical neutralization cells allow efficient use of chemical energy and low-grade heat from the surroundings to output 0.81 kWh electricity per m³ of hydrogen. Cell function can be rapidly switched to electricity output with a high peak power density up to 85.5 mW cm^-2 or spontaneous hydrogen production at a high rate up to 70.1 mol h^-1  m^-2 without breaking cell operation or changing cell configuration. Fast water desalination is simultaneously achieved at a high salt removal rate of 56.1 mol h^-1  m^-2 without an external electricity supply.

Caged-Cation-Induced Lattice Distortion in Bronze TiO2 for Cohering Nanoparticulate Hydrogen Evolution Electrocatalysts

Defect engineering provides a promising approach for optimizing the trade-off between support structures and active nanoparticles in heterojunction nanostructures, manifesting efficient synergy in advanced catalysis. Herein, a high density of distorted lattices and defects are successfully formed in bronze TiO₂ through caging alkali-metal Na cations in open voids (Na-TiO₂(B)), which could efficiently cohere nanoparticulate electrocatalysts toward alkaline hydrogen evolution reaction (HER). The RuMo bimetallic nanoparticles could directionally anchor on Na-TiO₂(B) with a certain angle of ∼22° due to elimination of the lattice mismatch, thus promoting uniform dispersion and small sizing of supported nanoparticles. Moreover, caging Na ions could significantly enhance the hydrophilicity of the substrate in RuMo/Na-TiO₂(B), leading to the strengthening synergy of water dissociation and hydrogen desorption. As expected, this Na-caged nanocomposite catalyst rich with structural perturbations manifests a 6.4-fold turnover frequency (TOF) increase compared to Pt/C. The study provides a paradigm for designing stable nano-heterojunction catalysts with lattice-distorted substrates by caging cations toward advanced electrocatalytic transformations.

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

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

Synergic Reaction Kinetics over Adjacent Ruthenium Sites for Superb Hydrogen Generation in Alkaline Media

Ruthenium (Ru)-based electrocatalysts as platinum (Pt) alternatives in catalyzing hydrogen evolution reaction (HER) are promising. However, achieving efficient reaction processes on Ru catalysts is still a challenge, especially in alkaline media. Here, the well-dispersed Ru nanoparticles with adjacent Ru single atoms on carbon substrate (Ru_1,n -NC) is demonstrated to be a superb electrocatalyst for alkaline HER. The obtained Ru_1,n -NC exhibits ultralow overpotential (14.8 mV) and high turnover frequency (1.25 H₂  s^-1 at -0.025 V vs reversible hydrogen electrode), much better than the commercial 40 wt.% Pt/C. The analyses reveal that Ru nanoparticles and single sites can promote each other to deliver electrons to the carbon substrate. Eventually, the electronic regulations bring accelerated water dissociation and reduced energy barriers of hydroxide/hydrogen desorption on adjacent Ru sites, then an optimized reaction kinetics for Ru_1,n -NC is obtained to achieve superb hydrogen generation in alkaline media. This work provides a new insight into the catalyst design in simultaneous optimizations of the elementary steps to obtain ideal HER performance in alkaline media.

Self-Co-Electrolysis for Co-Production of Phosphate and Hydrogen in Neutral Phosphate Buffer Electrolyte

The spontaneous reaction between Zn and H₂ O is of critical importance and could plausibly be used to produce H₂ gas, especially under neutral conditions. However, this reaction has long been overlooked owing to its sluggish kinetics and Zn consumption. Herein, a unique self-co-electrolysis system (SCES) is reported, which uses a Zn anode, a CoP-based catalytic cathode, and a neutral phosphate buffer solution (PBS) as the electrolyte. In this SCES, Zn is not only a sacrificial anode but also an important precursor of high-value-added NaZnPO₄ . Additionally, the composition and phase structure of NaZnPO₄ can be well regulated. In this study, a high-performance N,Cu-CoP/carbon cloth (CC) catalyst is synthesized to catalyze the cathodic hydrogen evolution reaction (HER) at an especially low overpotential of 64.7 mV at 10 mA cm^{- 2} . H₂ gas (13.7 mL cm^{- 2} h^{- 1} ) and NaZnPO₄ (3.73 mg cm^{- 2} h^{- 1} ) are obtained at the cathode and anode, respectively, in the N,Cu-CoP/CC||Zn SCES spontaneously. Moreover, the SCES has a favorable open-circuit voltage (OCV) of 0.79 V and a maximum power density of 1.83 mW cm^{- 2} . Density functional theory (DFT) calculations are performed to elucidate the electronic structure and HER catalytic mechanism of the N and Cu co-doped CoP catalysts.

Encapsulated RuP2-RuS2 nanoheterostructure with regulated interfacial charge redistribution for synergistically boosting hydrogen evolution electrocatalysis

Exploring cost-effective electrocatalysts with suitable hydrogen binding strength and rational micro/nano-architecture towards the hydrogen evolution reaction (HER) is crucial for energy technologies, yet remains a tough challenge. Herein we present the first instance of a nanoscale RuP₂-RuS₂ heterostructure encapsulated in N, P, and S co-doped porous carbon nanosheets (RuP₂-RuS₂/NPS-C) for boosting the HER. The synthesis involves the construction of a 2D core-shell structured precursor in which Ru³⁺-functionalized g-C₃N₄ is wrapped by poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) followed by pyrolysis. In this nanocomposite, the unique architecture with a highly dispersed embedded RuP₂-RuS₂ nanoheterostructure guarantees not only full exposure of the active sites with enhanced robustness but also smooth mass/charge transfer. More significantly, the experimental results and theoretical calculations reveal that coupling RuP₂ with RuS₂ to construct a heterointerface can induce charge redistribution, giving rise to optimized hydrogen adsorption energy for substantially accelerating the HER. This work provides a novel strategy to engineer high-performance Ru-based electrocatalysts by elegantly modulating the micro-/nano-architecture and interface coupling effect.

Key Role of Lorentz Excitation in the Electromagnetic-Enhanced Hydrogen Evolution Reaction

Alternating magnetic fields (AMFs) are recently demonstrated as a promising strategy to promote the electrochemical catalytic reactions. However, the underlying mechanisms are still an open question. In this work, we systematically investigated the influence of AMFs on the hydrogen evolution reaction (HER) by using a Fe-Co-Ni-P-B magnetic catalyst. The HER catalytic efficiency is boosted significantly by AMFs, with 27% increase in current density at 20 mT. This is attributed to the enhancement of charge-transfer efficiency by Lorentz interaction with a minor contribution from the heating effect. The high magnetic permeability and skin effect of electromagnetic eddy current for the Fe-Co-Ni-P-B electrode can magnify the Lorentz effect. These findings clarify the mechanism of AMF-enhanced HER catalytic activities and open a door for designing a high-efficiency electrocatalysis system.

Reversing the Nucleophilicity of Active Sites in CoP2 Enables Exceptional Hydrogen Evolution Catalysis

Precisely constructing the local configurations of active sites to achieve on-demand catalytic functions is highly critical yet challenging. Herein, an anion-deficient strategy to precisely capture Ru single atoms on the anion vacancies of CoP₂ (Ru-SA/Pv-CoP₂ ) is developed. Refined structural characterizations reveal that the Ru single atoms preferably bind to the anion vacancy sites and consequently build a superior catalytic surface with neighboring CoP and CoRu coordination states for the hydrogen evolution reaction (HER) catalysis. The prepared Ru-SA/Pv-CoP₂ nanowires exhibit an unprecedented overpotential of 17 mV at 10 mA cm^-2_geo , and the corresponding mass activity is 52.2 times higher than the benchmark Pt/C catalyst at the overpotential of 50 mV. Theoretical analysis illustrates that the introduced Ru-SAs can reverse electrons state distribution (from nucleophilic P sites to electrophilic Ru sites) and boost the activation of water molecules and hydrogen production. More importantly, such a construction strategy is also applicable for Pt single atom coupling, suggesting its generality in building catalytic sites. The capability to precisely construct active sites offers a powerful platform to manipulate the catalytic performance of HER catalysts and beyond.

Ir nanoclusters/porous N-doped carbon as a bifunctional electrocatalyst for hydrogen evolution and hydrazine oxidation reactions

One common iridium(III) complex was employed to facilely prepare ultrafine Ir nanoclusters embedded in porous N-doped carbon, which displayed significant bifunctional activity for both hydrogen evolution and hydrazine oxidation under alkaline conditions, enabling energy-efficient hydrogen production.

N, P-doped carbon supported ruthenium doped Rhenium phosphide with porous nanostructure for hydrogen evolution reaction using sustainable energies

Developing efficient and cost-effective catalysts for hydrogen evolution reaction (HER) is vital to hydrogen energy's commercial applications. In this study, N,P-doped carbon supported ruthenium (Ru) doped triruthenium tetraphosphide (Re₃P₄) (Ru-Re₃P₄/NPC) with porous nanostructure is prepared using the low-toxic melamine phosphate as the carbon and phosphorous source. The in-situ generated N,P-doped carbon layers play a pivotal role in regulating the electrocatalytic activity by avoiding the aggregation of the nanoparticles and increasing the specific surface area. Moreover, Ru doping contributes to the remarkable electrocatalytic performance of the prepared nanomaterials. Impressively, the as-synthesized Ru-Re₃P₄/NPC presents remarkable electrocatalytic performances toward HER with small overpotentials of 39 mV, 115 mV, and 88 mV to deliver 10 mA cm^-2 in alkaline, neutral, and acidic media. Moreover, the prepared electrocatalyst can drive water-splitting with a small potential of 1.45 V@10 mA cm^-2 and use sustainable energies, including solar, wind, and thermal, as electric resources. This work paves a novel and valuable way to enhance the electrocatalytic performances of metal phosphides.

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

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

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

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

Dual Nanoislands on Ni/C Hybrid Nanosheet Activate Superior Hydrazine Oxidation Assisted High-efficient H2 Production

Clean hydrogen evolution through electrochemical water splitting underpins various innovative approaches to the pursuit of sustainable energy conversion technologies, but it is blocked by the sluggish anodic oxygen evolution reaction (OER) during the water splitting. The hydrazine oxidation reaction (HzOR) has been considered to be one of the most promising substitute for OER to improve the efficiency of hydrogen evolution reaction (HER), however, the design of precise bifunctional catalysts which could integrate the high-efficient HER and HzOR activity is significant yet scarce. Herein, we originally construct novel dual nanoislands on Ni/C hybrid nanosheet array: one kind of island represents the part of bare Ni particle surface, while the other stands for the part of core-shell Ni@C structure (denoted as Ni-C HNSA), in which exposed Ni atoms and Ni-decorated carbon shell perform as active sites for HzOR and HER respectively. Simultaneously, the electrons of Ni in Ni@C islands will transfer to the C layer, causing the change of the electron density around the C layer, thereby accelerating the kinetics of HER. As a result, when the current density reaches 10 mA cm -2 , the overpotential of HER is merely 37 mV and the working potential of HzOR is as low as -20 mV. A two-electrode electrolyzer exhibits superb activity that only requiring an ultrasmall cell voltage of 0.2 V to achieve 50 mA cm -2 . This finding undoubtedly provides a new perspective for design of advanced bifunctional electrocatalysts, and propels the practical energy-saving H 2 generation techniques.

Platinum Modulates Redox Properties and 5-Hydroxymethylfurfural Adsorption Kinetics of Ni(OH)2 for Biomass Upgrading

Nickel hydroxide (Ni(OH)₂ ) is a promising electrocatalyst for the 5-hydroxymethylfurfural oxidation reaction (HMFOR) and the dehydronated intermediates Ni(OH)O species are proved to be active sites for HMFOR. In this study, Ni(OH)₂ is modified by platinum to adjust the electronic structure and the current density of HMFOR improves 8.2 times at the Pt/Ni(OH)₂ electrode compared with that on Ni(OH)₂ electrode. Operando methods reveal that the introduction of Pt optimized the redox property of Ni(OH)₂ and accelerate the formation of Ni(OH)O during the catalytic process. Theoretical studies demonstrate that the enhanced Ni(OH)O formation kinetics originates from the reduced dehydrogenation energy of Ni(OH)₂ . The product analysis and transition state simulation prove that the Pt also reduces adsorption energy of HMF with optimized adsorption behavior as Pt can act as the adsorption site of HMF. Overall, this work here provides a strategy to design an efficient and universal nickel-based catalyst for HMF electro-oxidation, which can also be extended to other Ni-based catalysts such as Ni(HCO₃ )₂ and NiO.

Anion Modulation of Pt-Group Metals and Electrocatalysis Applications

Pt-group metal (PGM) electrocatalysts with unique electronic structures and irreplaceable comprehensive properties play crucial roles in electrocatalysis. Anion engineering can create a series of PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) that provide a promising prospect for improving the electrocatalytic performance and use of Pt-group noble metals. This review seeks the electrochemical activity origin of anion-modulated PGM compounds, and systematically analyzes and summarizes their synthetic strategies and energy-relevant applications in electrocatalysis. Orientation towards the sustainable development of nonfossil resources has stimulated a blossoming interest in the design of advanced electrocatalysts for clean energy conversion. The anion-modulated strategy for Pt-group metals (PGMs) by means of anion engineering possesses high flexibility to regulate the electronic structure, providing a promising prospect for constructing electrocatalysts with superior activity and stability to satisfy a future green electrochemical energy conversion system. Based on the previous work of our group and others, this review summarizes the up-to-date progress on anion-modulated PGM compounds (such as RuP₂ , IrP₂ , PtP₂ , RuB₂ , Ru₂ B₃ , RuS₂ , etc.) in energy-related electrocatalysis from the origin of their activity and synthetic strategies to electrochemical applications including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), N₂ reduction reaction (NRR), and CO₂ reduction reaction (CO₂ RR). At the end, the key problems, countermeasures and future development orientations of anion-modulated PGM compounds toward electrocatalytic applications are proposed.

Structure-Tailored Non-Noble Metal-based Ternary Chalcogenide Nanocrystals for Pt-like Electrocatalytic Hydrogen Production

A facile microwave-assisted strategy was employed to synthesize Ni₃ Bi₂ S₂ nanocrystals. Variation in the synthesis conditions tuned the composition of monoclinic and orthorhombic phases of Ni₃ Bi₂ S₂ . The electrochemical hydrogen evolution activity of the catalyst with highest percentage of monoclinic phase demonstrated a negligible onset potential of only 24 mV close to that of state-of-the-art Pt/C with an overpotential as low as 88 mV. Density functional theory calculations predicted the monoclinic phase exhibit the lowest adsorption free energy corresponding to hydrogen adsorption ( Δ G ads H * ) and, therefore, the highest hydrogen evolution activity amongst the considered phases. The quasi-2D structure of monoclinic phase facilitated an increased charge-transfer between Ni and Bi, favoring the downward shift of the d-band center to enhance the catalytic activity.

Scalable Synthesis of Tungsten Disulfide Nanosheets for Alkali-Acid Electrocatalytic Sulfion Recycling and H2 Generation

WS₂ nanosheets hold great promise for a variety of applications yet faces a grand challenge in terms of large-scale synthesis. We report a reliable, scalable, and high-yield (>93 %) synthetic strategy to fabricate WS₂ nanosheets, which exhibit highly desirable electrocatalytic properties toward both the alkaline sulfion (S^2- ) oxidation reaction (SOR) and the acidic hydrogen evolution reaction (HER). The findings prompted us to develop a hybrid alkali-acid electrochemical cell with the WS₂ nanosheets as bifunctional electrode catalysts of alkaline anodic SOR and acidic cathodic HER. The proof-of-concept device holds promise for self-power or low-electricity electrolytic H₂ generation and environmentally friendly recycling of sulfion with enhanced electron utilization efficiency.

Solvent-free microwave synthesis of ultra-small Ru-Mo2C@CNT with strong metal-support interaction for industrial hydrogen evolution

Exploring a simple, fast, solvent-free synthetic method for large-scale preparation of cheap, highly active electrocatalysts for industrial hydrogen evolution reaction is one of the most promising work today. In this work, a simple, fast and solvent-free microwave pyrolysis method is used to synthesize ultra-small (3.5 nm) Ru-Mo₂C@CNT catalyst with heterogeneous structure and strong metal-support interaction in one step. The Ru-Mo₂C@CNT catalyst only exhibits an overpotential of 15 mV at a current density of 10 mA cm⁻², and exhibits a large turnover frequency value up to 21.9 s⁻¹ under an overpotential of 100 mV in 1.0 M KOH. In addition, this catalyst can reach high current densities of 500 mA cm⁻² and 1000 mA cm⁻² at low overpotentials of 56 mV and 78 mV respectively, and it displays high stability of 1000 h. This work provides a feasible way for the reasonable design of other large-scale production catalysts.

While H₂ could be a renewable fuel, the large-scale preparation of cheap, active electrocatalysts for large-scale production remains a challenge. Here, authors use a rapid, solvent-free microwave pyrolysis method to synthesize nanostructured catalysts for large-scale industrial H₂ production.

A Zeolitic-Imidazole Framework-Derived Trifunctional Electrocatalyst for Hydrazine Fuel Cells

Hydrazine fuel cells are promising sustainable power sources. However, the high price and limited reserves of noble metal catalysts that promote the sluggish cathodic and anodic electrochemical reactions hinder their practical applications. Reflecting the enhanced diffusion and improved kinetics of nanostructured non-noble metal electrocatalysts, we report an efficient zeolitic-imidazole framework-derived trifunctional electrocatalyst for hydrazine oxidation, oxygen, and hydrogen peroxide reduction. Experimental results and theoretical calculations corroborate that the nanocarbon architecture with abundant Co-N species enhances the electronic interaction and optimizes the energy barriers of anodic hydrazine oxidation and cathodic oxygen reduction. The resulting assembled hydrazine-oxygen fuel cell yields a cell voltage and power density of 0.74 V and 20.5 mW cm^-2, respectively. Moreover, benefiting from the liquid-liquid diffusion, the hydrazine-hydrogen peroxide cell shows a boosted cell voltage and power density, corresponding to 1.68 V and 41.0 mW cm^-2. This work offers a highly active non-noble metal multifunctional electrocatalyst with a pioneering diffusion philosophy in the liquid electrochemical cells.

Chemical Transformations of Anisotropic Platelets and Spherical Nanocrystals

ConspectusInorganic nanocrystal design has been continuously evolving with a better understanding of the chemical reaction mechanisms between chemical stimuli and nanocrystals. Under certain conditions, molecular compounds can be effective as chemical stimuli to induce transformative reactions of nanocrystals toward new materials that would differ in geometric shape, composition, and crystallographic structure. To explore such evolutionary processes, two-dimensional (2D) layered transition-metal chalcogenide (TMC) nanostructures are an interesting structural platform because they not only exhibit unique transformation pathways due to their structural anisotropy but also present new opportunities for improved material properties for potential applications such as catalysis and energy conversion and storage. The high surface area/volume ratio, interlayer van der Waals (vdW) spacing, and different coordination states between the unsaturated edges and the fully saturated basal planes of the chalcogens are characteristic of 2D layered TMC nanostructures, which subsequently lead to anisotropic chemical processes during chemical transformations, such as regioselective reactions at the interfacial boundaries in the pathways for either porous or solid heteronanostructures. In this Account, we first discuss the chemical reactivity of 2D layered TMC nanostructures. By categorizing the external stimuli in terms of chemical principles, such as Lewis acid-base chemistry, a desirable regioselective chemical reaction can occur with controlled reactivity. In association with the knowledge obtained from the nanoscale chemical reactivity of 2D layered nanocrystals, similar efforts in other important morphologies such as 1D and isotropic 0D nanocrystals are introduced. For instance, for 1D and 0D metal oxide nanocrystals, the effects of molecular stimuli on the atomic-level changes in the crystal lattice are demonstrated, eventually leading to a variety of shape transformations.

In Situ Electrochemical Fabrication of Ultrasmall Ru-Based Nanoparticles for Robust N2H4 Oxidation

Ultrasmall Ru nanoparticles is expected as a potential alternative to Pt for efficient hydrazine oxidation (HzOR). However, preparation of ultrasmall and well-distributed Ru nanoparticles usually suffered from the steps of modification of supports, coordination, reduction with strong reducing reagents (e.g., NaBH₄) or pyrolysis, imposing the complexity. Based on the self-reducibility of C-OH group and physical adsorption ability of commercial Ketjen black (KB), we developed an efficient, stable and robust Ru-based electrocatalyst (A-Ru-KB) by coupling impregnation of KB in RuCl₃ solution and simple in situ electrochemical activation strategy, which endowed the formation of ultrasmall and well-distributed Ru nanoparticles. Benefiting from an enhanced exposure of Ru sites and the faster mass transport, A-Ru-KB achieved 63.4 and 3.9-fold enhancements of mass activity compared with Pt/C and Ru/C, respectively, accompanied by a ∼144 mV lower onset potential and faster catalytic kinetics than Pt/C. In the hydrazine fuel cell, the open-circuit voltage and maximal mass power density of A-Ru-KB was 130 mV and ∼3.8-fold higher than those of Pt/C, respectively, together with the long-term stability. This work would provide a facile and sustainable approach for large-scale production of other robust metal (electro)catalysts with ultrasmall nanosize for various energy conversion and electrochemical organic synthesis.

Vanadium Substitution Steering Reaction Kinetics Acceleration for Ni3N Nanosheets Endows Exceptionally Energy-Saving Hydrogen Evolution Coupled with Hydrazine Oxidation

Designing highly active transition-metal-based electrocatalysts for energy-saving electrochemical hydrogen evolution coupled with hydrazine oxidation possesses more economic prospects. However, the lack of bifunctional electrocatalysts and the absence of intrinsic structure-property relationship research consisting of adsorption configurations and dehydrogenation behavior of N₂H₄ molecules still hinder the development. Now, a V-doped Ni₃N nanosheet self-supported on Ni foam (V-Ni₃N NS) is reported, which presents excellent bifunctional electrocatalytic performance toward both hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER). The resultant V-Ni₃N NS achieves an ultralow working potential of 2 mV and a small overpotential of 70 mV at 10 mA cm^-2 in alkaline solution for HzOR and HER, respectively. Density functional theory calculations reveal that the vanadium substitution could effectively modulate the electronic structure of Ni₃N, therefore facilitating the adsorption/desorption behavior of H* for HER, as well as boosting the dehydrogenation kinetics for HzOR.

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.

Amorphous Ta2O5-supported Ru as an efficient electrocatalyst for selective hydrogenation of cinnamaldehyde with water as the hydrogen source

Amorphous Ta2O5-supported Ru as an efficient electrocatalyst for electrocatalytic selective hydrogenation of cinnamaldehyde.