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

Bimetallic Metal Sites in Metal-Organic Frameworks Facilitate the Production of 1-Butene from Electrosynthesized Ethylene

Converting CO2 to synthetic hydrocarbon fuels is of increasing interest. In light of progress in electrified CO2 to ethylene, we explored routes to dimerize to 1-butene, an olefin that can serve as a building block to ethylene longer-chain alkanes. With goal of selective and active dimerization, we investigate a series of metal-organic frameworks having bimetallic catalytic sites. We find that the tunable pore structure enables optimization of selectivity and that periodic pore channels enhance activity. In a tandem system for the conversion of CO2 to 1-C4H8, wherein the outlet cathodic gas from a CO2-to-C2H4 electrolyzer is fed directly (via a dehumidification stage) into the C2H4 dimerizer, we study the highest-performing MOF found herein: M' = Ru and M″ = Ni in the bimetallic two-dimensional M'2(OAc)4M″(CN)4 MOF. We report a 1-C4H8 production rate of 1.3 mol gcat-1 h-1 and a C2H4 conversion of 97%. From these experimental data, we project an estimated cradle-to-gate carbon intensity of -2.1 kg-CO2e/kg-1-C4H8 when CO2 is supplied from direct air capture and when the required energy is supplied by electricity having the carbon intensity of wind.

Correlating Single-Atomic Ruthenium Interdistance with Long-Range Interaction Boosts Hydrogen Evolution Reaction Kinetics

Correlated single-atom catalysts (c-SACs) with tailored intersite metal-metal interactions are superior to conventional catalysts with isolated metal sites. However, precise quantification of the single-atomic interdistance (SAD) in c-SACs is not yet achieved, which is essential for a crucial understanding and remarkable improvement of the correlated metal-site-governed catalytic reaction kinetics. Here, three Ru c-SACs are fabricated with precise SAD using a planar organometallic molecular design and π-π molecule-carbon nanotube confinement. This strategy results in graded SAD from 2.4 to 9.3 Å in the Ru c-SACs, wherein tailoring the Ru SAD into 7.0 Å generates an exceptionally high turnover frequency of 17.92 H2 s-1 and a remarkable mass activity of 100.4 A mg-1 under 50 and 100 mV overpotentials, respectively, which is superior to all the Ru-based catalysts reported previously. Furthermore, density functional theory calculations confirm that Ru SAD has a negative correlation with its d-band center owing to the long-range interactions induced by distinct local atomic geometries, resulting in an appropriate electrostatic potential and the highest catalytic activity on c-SACs with 7.0 Å Ru SAD. The present study promises an attractive methodology for experimentally quantifying the metal SAD to provide valuable insights into the catalytic mechanism of c-SACs.

Fe Single-Atom Catalyst for Cost-Effective yet Highly Efficient Heterogeneous Fenton Catalysis

High energy consumption in pyrolyzing precursors for catalyst preparation would limit the application of nitrogen-doped carbon-based single-atom catalysts in actual pollutant remediation. Herein, we report an Fe single atom (7.67 wt %) loaded polyaniline catalyst (Fe-PANI) prepared via a simple impregnation process without pyrolysis. Both experimental characterizations and density functional theory calculations demonstrated that isolated -N═ group sites can fasten Fe atoms through Fe-N coordination in PANI, leading to a high stability of Fe atoms in a heterogeneous Fenton reaction. Highly dispersive yet dense -N═ groups in PANI can be protonated to be adsorption sites, which largely reduce the migration distance between reactive radicals and organics. More significantly, frontier molecular orbitals and spin-density distributions reveal that electrons can transfer from reduction groups of PANI to an Fe(III) site to accelerate its reduction. As a result, a remarkably boosted degradation behavior of organics under near-neutral conditions (pH 6), with low H₂O₂ concentration, was achieved. This cost-effective Fe-PANI catalyst with high catalytic activity, stability, and adsorption performance has great potential for industrial-level wastewater treatment.

Synergetic Function of the Single-Atom Ru-N4 Site and Ru Nanoparticles for Hydrogen Production in a Wide pH Range and Seawater Electrolysis

Hydrogen production by water splitting and seawater electrolysis is a promising alternative to develop clean hydrogen energy. The construction of high-efficiency and durable electrocatalysts for the hydrogen evolution reaction (HER) in a wide pH range and seawater is critical to overcoming the sluggish kinetic process. Herein, we develop an efficient catalytic material composed of a single-atom Ru-N₄ site and Ru nanoparticles anchored on nitrogen-doped carbon (Ru_1+NPs/N-C) through the coordination-pyrolysis strategy of the melamine formaldehyde resin. The Ru_1+NPs/N-C catalyst shows outstanding HER activity with the smallest overpotentials, the lowest Tafel slopes, the highest mass activity and turnover frequency, as well as excellent stability in both acidic and alkaline media. Moreover, Ru_1+NPs/N-C shows comparable hydrogen production performance and a higher faradic efficiency to 20% Pt/C in natural seawater and artificial simulated seawater. Theoretical calculations demonstrate that the strong synergistic effects between the Ru-N₄ site and Ru nanoparticles modify the electronic structure to accelerate the HER kinetics. Ru nanoparticles can effectively realize dissociation of H₂O to generate adsorbed hydrogen and also promote the single-atom Ru-N₄ site to combine adsorbed hydrogen to H₂ and desorption. This work provides a new perspective for designing high-efficiency hydrogen production electrocatalysts for large-scale seawater electrolysis.

Competitive Coordination-Oriented Monodispersed Ruthenium Sites in Conductive MOF/LDH Hetero-Nanotree Catalysts for Efficient Overall Water Splitting in Alkaline Media

Rational exploration of efficient, inexpensive, and robust electrocatalysts is critical for the efficient water splitting. Conjugated conductive metal-organic frameworks (cMOFs) with multicomponent layered double hydroxides (LDHs) to construct bifunctional heterostructure catalysts are considered as an efficient but complicated strategy. Here, the fabrication of a cMOF/LDH hetero-nanotree array catalyst (CoNiRu-NT) coupled with monodispersed ruthenium (Ru) sites via a controllable grafted-growth strategy is reported. Rich-amino hexaiminotriphenylene linkers coordinate with the LDH nanotrunk to form cMOF nanobranches, providing numerous anchoring sites to precisely confine and stabilize RuN₄ sites. Moreover, monodispersed and reduced Ru moieties facilitate H₂ O adsorption and dissociation, and the heterointerface between the cMOF and the LDH further modifies the chemical and electronic structures. Optimized CoNiRu-NT displays a significant increase in electrochemical water-splitting properties in alkaline media, affording low overpotentials of 22 mV at 10 mA cm^-2 and 255 mV at 20 mA cm^-2 for the hydrogen evolution reaction and oxygen evolution reaction, respectively. In an actual electrochemical system, CoNiRu-NT drives an overall water splitting at a low cell voltage of 1.47 V to reach 10 mA cm^-2 . This performance is comparable to that of pure noble-metal-based materials and superior to most reported MOF-based catalysts.

In Situ/Operando Insights into the Stability and Degradation Mechanisms of Heterogeneous Electrocatalysts

The further commercialization of renewable energy conversion and storage technologies requires heterogeneous electrocatalysts that meet the exacting durability target. Studies of the stability and degradation mechanisms of electrocatalysts are expected to provide important breakthroughs in stability issues. Accessible in situ/operando techniques performed under realistic reaction conditions are therefore urgently needed to reveal the nature of active center structures and establish links between the structural motifs in a catalyst and its stability properties. This review highlights recent research advances regarding in situ/operando techniques and improves the understanding of the stabilities of advanced heterogeneous electrocatalysts used in a diverse range of electrochemical reactions; it also proposes some degradation mechanisms. The review concludes by offering suggestions for future research.

Polyaniline coating enables electronic structure engineering in Fe3O4to promote alkaline oxygen evolution reaction

The electronic structure of active sites is of importance for catalysts to achieve an optimized interaction with the intermediates. In this study, a unique organic-inorganic hybrid oxygen evolution reaction electrocatalyst composed of electrochemically inactive conducting polyaniline (PANI) and non-precious Fe-based oxide Fe₃O₄is presented. PANI molecules werein situloaded on Fe₃O₄nanoparticles through an efficient and simple process under mild conditions. The electronic structure of Fe₃O₄was modulated by creating a strong interaction with PANI molecules, leading to enhanced activity and stability of the catalyst to achieve 10 mA cm^-2geometrical current density at overpotential of 265 mV in 1 M aqueous KOH solution. This work demonstrates that a highly efficient electrocatalyst can be achieved by molecular modification and provides a novel strategy for the optimization of the inactive non-precious catalysts.

Bifunctional atomically dispersed ruthenium electrocatalysts for efficient bipolar membrane water electrolysis

Atomically dispersed catalysts (ADCs) have recently drawn considerable interest for use in water electrolysis to produce hydrogen, because they allow for maximal utilization of metal species, particularly the expensive and...

Nanoscaled and Atomic Ruthenium Electrocatalysts Confined Inside Super-Hydrophilic Carbon Nanofibers for Efficient Hydrogen Evolution Reaction

A series of Ru-based catalysts have been developed for the hydrogen evolution reaction (HER) by the facile impregnation of copious and eco-friendly bacterial cellulose (BC) with Ru(bpy)₃ Cl₂ (bpy = 2,2'-bipyridine) followed by pyrolysis. After the oxidation and molecular recomposition processes that occur within the BC precursors during pyrolysis, sub-2 nm Ru nanoparticles (NPs) and atomic Ru species confined within surface-oxidized N-doped carbon nanofibers (CNFs) can be observed in the derived catalysts. The surface oxidation of CNFs leads the derived catalysts with super hydrophilicity and water-absorbing capacity, and also provides dimensional confinement for the nanoscaled and atomic Ru species. With these added structural advantages and the component synergy, the derived catalysts show superior HER activities, for which the overpotentials are as low as 19.6 mV (1 m KOH) and 55.0 mV (0.5 m H₂ SO₄ ) for the most active case at the current density of 10 mA cm^-2 . Moreover, superior HER activity can be also achieved for the catalysts derived with a wide range of Ru loadings. Finally, the influence of Ru NP size on HER activity is investigated by density functional theory simulations. This method provides a reliable protocol for preparing highly active HER catalysts for scale-up applications.

Engineering Ruthenium-Based Electrocatalysts for Effective Hydrogen Evolution Reaction

The investigation of highly effective, durable, and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is a prerequisite for the upcoming hydrogen energy society. To establish a new hydrogen energy system and gradually replace the traditional fossil-based energy, electrochemical water-splitting is considered the most promising, environmentally friendly, and efficient way to produce pure hydrogen. Compared with the commonly used platinum (Pt)-based catalysts, ruthenium (Ru) is expected to be a good alternative because of its similar hydrogen bonding energy, lower water decomposition barrier, and considerably lower price. Analyzing and revealing the HER mechanisms, as well as identifying a rational design of Ru-based HER catalysts with desirable activity and stability is indispensable. In this review, the research progress on HER electrocatalysts and the relevant describing parameters for HER performance are briefly introduced. Moreover, four major strategies to improve the performance of Ru-based electrocatalysts, including electronic effect modulation, support engineering, structure design, and maximum utilization (single atom) are discussed. Finally, the challenges, solutions and prospects are highlighted to prompt the practical applications of Ru-based electrocatalysts for HER.

Fragment-interconnected nitrogen-doped porous carbon nanosheets loaded with platinum group metals for highly boosted hydrogen evolution reaction in alkaline solution

The rational design and preparation of advanced electrocatalysts for the hydrogen evolution reaction (HER) under alkaline conditions is the key to achieving sustainable hydrogen production. Herein, a new type of nitrogen-doped porous carbon nanosheets (NPCN) loaded with platinum group metals (Pd, Pt or Ru) were prepared. The introduction of melamine not only realized the doping of N-species, but also optimized the morphology and surface functional groups of the prepared catalysts. The prepared Pd-NPCN, Pt-NPCN and Ru-NPCN with a metal loading of about 10 wt% showed outstanding HER activity (21, 9 and 11 mv at 10 mA cm^-2 current density), small Tafel slopes (49, 30 and 30 mV dec^-1) and good stability in 1.0 M KOH. In addition, the mechanism of the introduction of melamine to improve the catalytic performance of HER was also discussed. Therefore, this work provides promising alternatives to traditional Pt-based catalysts, and is instructive for the design of high-efficiency alkaline HER catalysts.

Uniformly Dispersed Ru Nanoparticles Constructed by In Situ Confined Polymerization of Ionic Liquids for the Electrocatalytic Hydrogen Evolution Reaction

Design and development of cost-effective electrocatalysts with high efficiency and stability for scalable and sustainable hydrogen production through water splitting is still challenging. Herein, with the aid of divinyl functionalized ionic liquids, uniformly distributed Ru nanoparticles (NPs) on nitrogen-doped carbon frameworks are obtained via an in situ confined polymerization strategy. Attributed to the unique lamellar structure and confinement effect of carbon supports, the optimized homo-PIL-Ru/C-600 (with Ru 10 wt%) catalyst exhibits superior catalytic efficiency for the hydrogen evolution reaction with the overpotential of only 16 mV at a current density of 10 mA cm^-2 and the corresponding Tafel slope of only 42 mV dec^-1 . Moreover, the performance can be well reserved even after 10 000 cycles, demonstrating excellent stability and promising potentials for industrial application. This work not only provides a facile approach for the preparation of highly efficient Ru-based catalysts, but also guides the synthesis of other highly dispersed metallic NPs for special applications.

Modulating electronic structure of metal-organic frameworks by introducing atomically dispersed Ru for efficient hydrogen evolution

Developing high-performance electrocatalysts toward hydrogen evolution reaction is important for clean and sustainable hydrogen energy, yet still challenging. Herein, we report a single-atom strategy to construct excellent metal-organic frameworks (MOFs) hydrogen evolution reaction electrocatalyst (NiRu0.13-BDC) by introducing atomically dispersed Ru. Significantly, the obtained NiRu0.13-BDC exhibits outstanding hydrogen evolution activity in all pH, especially with a low overpotential of 36 mV at a current density of 10 mA cm-2 in 1 M phosphate buffered saline solution, which is comparable to commercial Pt/C. X-ray absorption fine structures and the density functional theory calculations reveal that introducing Ru single-atom can modulate electronic structure of metal center in the MOF, leading to the optimization of binding strength for H2O and H*, and the enhancement of HER performance. This work establishes single-atom strategy as an efficient approach to modulate electronic structure of MOFs for catalyst design.

Discovery and Facile Synthesis of a New Silicon Based Family as Efficient Hydrogen Evolution Reaction Catalysts: A Computational and Experimental Investigation of Metal Monosilicides

A new family of transition-metal monosilicides (MSi, M = Ti, Mn, Fe, Ru, Ni, Pd, Co, and Rh) electrocatalysts with superior electrocatalytic performance of hydrogen evolution is reported, based on the computational and experimental results. It is proposed that these MSi can be synthesized within several minutes by adopting the arc-melting method. The previously reported RuSi is not only fabricated more readily but eventually explored 8 MSi that can be good hydrogen evolution reaction catalysts. Silicides then can be another promising electrocatalysts family as carbides, wherein carbon has the same electronic configuration as silicon. All explored silicides electrodes exhibited low overpotentials (34-54 mV at 10 mA cm^-2 ) with Tafel slopes from 23.6 to 32.3 mV dec^-1 , which are comparable to that of the commercial 20 wt% Pt/C (37 mV, 26.1 mV dec^-1 ). First-principles calculations demonstrated that the superior performance can be attributed to the high catalytic reactivity per site that can even function at high hydrogen coverages (≈100%) on multiple low surface energy facets. The work sheds light on a new class of electrocatalysts for hydrogen evolution, with earth-abundant and inexpensive silicon-based compounds.

Synergistic Catalysis of Binary RuP Nanoclusters on Nitrogen-Functionalized Hollow Mesoporous Carbon in Hydrogen Production from the Hydrolysis of Ammonia Borane

Exploring highly efficient nanocatalysts for hydrogen (H₂) production from catalytic hydrolysis of ammonia borane (AB) under ambient conditions and further unveiling their catalytic mechanism are of critical importance for renewable energy conversion technologies but remain big challenges. Herein, ultrafine binary RuP alloy nanoclusters homogeneously encapsulated onto nitrogen-functionalized hollow mesoporous carbon supports (RuP@NHMCs) are reported as a high-performance platinum (Pt)-free nanocatalyst for catalytic hydrolysis of AB at room temperature. Remarkable catalytic activity with a very high turnover frequency of 1774 mol_H2 mol_Ru^-1 min^-1 and a low activation energy of 36.3 kJ mol^-1 is observed based on compositional and structural synergies of RuP@NHMCs. Results of control experiments and catalytic kinetics studies reveal that the rate-determining step of catalytic hydrolysis of AB is the oxidation cleavage of a covalently stable H-OH bond, while RuP@NHMCs result in multiple electronic, functional, size, and support effects that kinetically accelerate the cleavage of attacked H-OH. Furthermore, RuP@NHMCs exhibit a good catalytic activity with a high yield of >99% for tandem hydrogenation of nitroarenes coupled with the hydrolysis of AB. We strongly believe that the catalyst design principle reported here could provide a new opportunity for synthesizing other Pt-free high-performance nanocatalysts.

Promotion of hydrogen evolution catalysis by ordered hierarchically porous electrodes

Ru-Based ordered hierarchically porous electrodes promote fast mass transfer and diffusion for hydrogen evolution under high current densities.

A Novel Heterostructure Based on RuMo Nanoalloys and N-doped Carbon as an Efficient Electrocatalyst for the Hydrogen Evolution Reaction

Heterostructures exhibit considerable potential in the field of energy conversion due to their excellent interfacial charge states in tuning the electronic properties of different components to promote catalytic activity. However, the rational preparation of heterostructures with highly active heterosurfaces remains a challenge because of the difficulty in component tuning, morphology control, and active site determination. Herein, a novel heterostructure based on a combination of RuMo nanoalloys and hexagonal N-doped carbon nanosheets is designed and synthesized. In this protocol, metal-containing anions and layered double hydroxides are employed to control the components and morphology of heterostructures, respectively. Accordingly, the as-made RuMo-nanoalloys-embedded hexagonal porous carbon nanosheets are promising for the hydrogen evolution reaction (HER), resulting in an extremely small overpotential (18 mV), an ultralow Tafel slope (25 mV dec^-1 ), and a high turnover frequency (3.57 H₂ s^-1 ) in alkaline media, outperforming current Ru-based electrocatalysts. First-principle calculations based on typical 2D N-doped carbon/RuMo nanoalloys heterostructures demonstrate that introducing N and Mo atoms into C and Ru lattices, respectively, triggers electron accumulation/depletion regions at the heterosurface and consequently reduces the energy barrier for the HER. This work presents a convenient method for rational fabrication of carbon-metal heterostructures for highly efficient electrocatalysis.

Ru catalyst supported on nitrogen-doped nanotubes as high efficiency electrocatalysts for hydrogen evolution in alkaline media

Due to the potential application in the future energy conversion system, there is an increasing demand for efficient, stable and cheap platinum-free catalysts for hydrogen evolution. However, it is still a great challenge to develop electrocatalysts with high activity similar to platinum or even higher, especially those that can work under alkaline conditions. Ruthenium (Ru), as a cheap substitute for platinum, has been studied as a feasible substitute for (HER) catalyst for hydrogen evolution reaction. In this paper, we designed and developed a novel Ru catalyst (Ru@CNT) supported on nitrogen-doped carbon nanotubes. Electrochemical tests show that even under alkaline conditions (1 M KOH), Ru@CNT still shows excellent catalytic performance and good durability. It only needs 36.69 mV overpotential to reach a current density of 10 mA cm-2, and its Tafel slope is 28.82 mV dec-1. The catalytic performance of the catalyst is comparable to that of 20% Pt/C. The significant activity is mainly attributed to the chelation of highly dispersed ruthenium atoms on nitrogen-doped carbon nanotubes. Secondly, the one-dimensional pore structures supported by nitrogen heterocarbon nanotubes can provide more opportunities for active centers. Excellent HER performance makes Ru@CNT electrocatalyst have a broad application prospect in practical hydrogen production.

Geometric Structure and Electronic Polarization Synergistically Boost Hydrogen Evolution Kinetics in Alkaline Medium

Efficient electrocatalysts for the hydrogen evolution reaction (HER) are significant for the utilization of hydrogen as a fuel, particularly under alkaline conditions. However, the sluggish kinetics of HER remains a challenge. Here we demonstrate an efficient HER catalyst comprising Ru and AgCl nanoparticles anchored on Ag nanowires (Ru/AgCl@Ag), which delivers a low overpotential of 12 mV at 10 mA cm^-2 and a Tafel slope of 38 mV decade^-1. A high mass activity of 214 mA mg^-1 at an overpotential of 25 mV and a long-term durability in 1.0 M KOH are observed. In combination with computational simulations, we find that the high electronegativity of chlorine in AgCl and d-band electrons from Ru synergistically destabilize the water molecule and modulate H adsorption/desorption on the surface of Ru/AgCl@Ag, respectively. This work opens a promising avenue for the facile design and application of highly active and stable composite electrocatalysts toward water splitting.

Mesoporous Iron-doped MoS2/CoMo2S4 Heterostructures through Organic-Metal Cooperative Interactions on Spherical Micelles for Electrochemical Water Splitting

Mesoporous metal sulfide hybrid (meso-MoS₂/CoMo₂S₄) materials via a soft-templating approach using diblock copolymer polystyrene-block-poly(acrylic acid) micelles are reported. The formation of the meso-MoS₂/CoMo₂S₄ heterostructures is based on the sophisticated coassembly of dithiooxamide and metal precursors (i.e., Co²⁺, PMo₁₂), which are subsequently annealed in nitrogen atmosphere to generate the mesoporous material. Decomposing the polymer leaves behind mesopores throughout the spherical MoS₂/CoMo₂S₄ hybrid particles, generating numerous electrochemical active sites in a network of pores that enable faster charge transfer and mass/gas diffusion that enhance the electrocatalytic performance of MoS₂/CoMo₂S₄. Doping the spherical meso-MoS₂/CoMo₂S₄ heterostructures with iron improves the electronic properties of the hybrid meso-Fe-MoS₂/CoMo₂S₄ material and consequently results in its superior electrochemical activities for both hydrogen evolution reaction and oxygen evolution reaction.

Highly-dispersed ruthenium precursors via a self-assembly-assisted synthesis of uniform ruthenium nanoparticles for superior hydrogen evolution reaction

For the first time, highly-dispersed ruthenium precursors via a hydrogen-bond-driven melamine–cyanuric acid supramolecular complex (denoted CAM) self-assembly-assisted synthesis of uniform ruthenium nanoparticles with superior HER performance under both acidic and alkaline conditions are reported. Electrochemical tests reveal that when the current density is −10 mA cm⁻², the optimal Ru/CNO electrocatalyst could express low overpotentials of −18 mV and −46 mV, low Tafel slopes of 46 mV dec⁻¹ and 100 mV dec⁻¹, in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. The remarkable HER performance could be attributed to uniform ruthenium with the aid of highly dispersed ruthenium precursors (Ru–CAM) and subsequent annealing results in uniform ruthenium nanoparticles.

Highly dispersed ruthenium precursors via a supramolecular self-assembly assisted synthesis of uniform ruthenium nanoparticles with excellent HER performance.

Confining Sub-Nanometer Pt Clusters in Hollow Mesoporous Carbon Spheres for Boosting Hydrogen Evolution Activity

Electrochemical water splitting is considered as a promising approach to produce clean and sustainable hydrogen fuel. As a new class of nanomaterials with high ratio of surface atoms and tunable composition and electronic structure, metal clusters are promising candidates as catalysts. Here, a new strategy is demonstrated to synthesize active and stable Pt-based electrocatalysts for hydrogen evolution by confining Pt clusters in hollow mesoporous carbon spheres (Pt₅ /HMCS). Such a structure would effectively stabilize the Pt clusters during the ligand removal process, leading to remarkable electrocatalytic performance for hydrogen production in both acidic and alkaline solutions. Particularly, the optimal Pt₅ /HMCS electrocatalyst exhibits 12 times the mass activity of Pt in commercial Pt/C catalyst with similar Pt loading. This study exemplifies a simple yet effective approach to improve the cost effectiveness of precious-metal-based catalysts with stabilized metal clusters.

pH universal Ru@N-doped carbon catalyst for efficient and fast hydrogen evolution

An efficient and robust hydrogen evolution electrocatalyst of Ru nanoparticles embedded in N-doped carbon was obtained by using Bu₄N[Ru(N)Cl₄] and Na₄EDTA as precursors. It exhibits excellent catalytic activity in alkaline solutions and good performance in acidic media.

Modulation of Inverse Spinel Fe3 O4 by Phosphorus Doping as an Industrially Promising Electrocatalyst for Hydrogen Evolution

Fe-based oxides have been seldom reported as electrocatalysts for the hydrogen evolution reaction (HER), limited by their weak intrinsic activity and conductivity. Herein, phosphorus doping modulation is used to construct inverse spinel P-Fe₃ O₄ with dual active sites supported on iron foam (P-Fe₃ O₄ /IF) for alkaline HER with an extremely low overpotential of 138 mV at 100 mA cm^-2 . The obtained inverse spinel Fe-O-P derived from controllable phosphorization can provide an octahedral Fe site and O atom, which bring about the unusual dissociation mechanisms of two water molecules to greatly accelerate the proton supply in alkaline media. Meanwhile, the ΔG_H of the P atom in Fe-O-P as an active site is theoretically calculated to be 0.01 eV. Notably, the NiFe LDH/IF⁽⁺⁾ ||P-Fe₃ O₄ /IF^(-) couple achieves an onset potential of 1.47 V (vs RHE) for overall water splitting, with excellent stability for more than 1000 h at a current density of 1000 mA cm^-2 , and even for 25 000 s at 10 000 mA cm^-2 in 6.0 m KOH at 60 °C. The excellent catalyst stability and low-cost merits of P-Fe₃ O₄ /IF may hold promise for industrial hydrogen production. This work may reveal a new design strategy of earth-abundant materials for large-scale water splitting.

Engineering ultrasmall metal nanoclusters for photocatalytic and electrocatalytic applications

In view of many of the fundamental properties of ultrasmall noble metal nanoclusters progressively being uncovered, it has become increasingly clear that this class of materials has enormous potential for photocatalytic and electrocatalytic applications due to their unique electronic and optical properties. In this Minireview, we highlight the key electronic and optical properties of metal nanoclusters which are essential to photocatalysis and electrocatalysis. We further use these properties as the basis for our discussion to map out directions or principles for the rational design of high performance photocatalysts and electrocatalysts, highlighting several successful attempts along this direction.

Subnano Amorphous Fe-Based Clusters with High Mass Activity for Efficient Electrocatalytic Oxygen Reduction Reaction

The development of cost-effective and efficient oxygen-relative electrocatalysts with high mass activity is extremely critical for modern sustainable fuel cells. Here, we present a new type of subnano amorphous transition-metal clusters supported on a hierarchical carbon framework as a promising oxygen reduction reaction (ORR) electrocatalyst, synthesized by a novel "amino-induced spatial confinement" strategy. This developed Fe subnano-cluster/3D-C could deliver outstanding ORR performance with a large mass activity of ∼8600 A g_Fe^-1 at a half-wave potential of 0.92 V, ∼10 times that of the benchmarking Pt/C electrocatalyst. The atomic characterizations and theoretical calculations jointly reveal the robust surface-covalent Fe-N bonds, and the synergistic effect of hetero Fe^2+/0 species is essentially beneficial for the adsorption of *O₂ and the formation of key *O intermediate during the ORR process, contributing to high oxygen-relative electrocatalytic activity for subnano amorphous Fe clusters.

Operando Insight into the Oxygen Evolution Kinetics on the Metal-Free Carbon-Based Electrocatalyst in an Acidic Solution

Operando insight into the catalytic kinetics under working conditions is important for further rationalizing the design of advanced catalysts toward efficient renewable energy applications. Here, we enable a ubiquitous carbon material as an efficient acidic oxygen evolution reaction (OER) electrocatalyst, synthesized via a facile and controllable "amino-assisted polymerization and carbonization" strategy. This as-developed metal-free amino-rich hierarchical-network carbon (amino-HNC) framework directly supported on carbon paper can catalyze OER at a quite low overpotential of 281 mV and a small Tafel slope of 96 mV dec^-1 in an acid solution, and maintain ∼98% of its initial catalytic activity after 100 h oxygen evolution operation. By using the operando synchrotron infrared spectroscopy, a crucial structurally evolved H₂N-(*O-C)-C, formed by adsorbing the *O intermediate on the active H₂N-C═C moiety, is observed on amino-HNC electrocatalysts during the OER process in the acid medium. Furthermore, theoretical calculations reveal that the optimization of the sp² electronic structure of C═C by amino radicals could effectively lower the kinetic formation barrier of the *O intermediate on the H₂N-C═C moiety, contributing to a prominent acidic oxygen-involved catalysis.

Ruthenium Nanoparticles for Catalytic Water Splitting

Both global warming and limited fossil resources make the transition from fossil to solar fuels an urgent matter. In this regard, the splitting of water activated by sunlight is a sustainable and carbon-free new energy conversion scheme able to produce efficient technological devices. The availability of appropriate catalysts is essential for the proper kinetics of the two key processes involved, namely, the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). During the last decade, ruthenium nanoparticle derivatives have emerged as true potential substitutes for the state-of-the-art platinum and iridium oxide species for the HER and OER, respectively. Thus, after a summary of the most common methods for catalyst benchmarking, this review covers the most significant developments of ruthenium-based nanoparticles used as catalysts for the water-splitting process. Furthermore, the key factors that govern the catalytic performance of these nanocatalysts are discussed in view of future research directions.

High-Performance Ru@C4N Electrocatalyst for Hydrogen Evolution Reaction in Both Acidic and Alkaline Solutions

We report a high-performance Ru@C₄N electrocatalyst for the hydrogen evolution reaction (HER) in both acidic and alkaline solutions. This catalyst is synthesized by annealing a complex of a covalent organic framework compound coordinated with ruthenium synthesized by a "one-pot" solvothermal method. This Ru@C₄N catalyst shows excellent electrocatalytic activity toward the hydrogen evolution reaction (HER) in both acidic and alkaline solutions with very low overpotentials at 10 mA/cm² (6 mV in 0.5 M H₂SO₄ solution; 7 mV in 1.0 M KOH solution), which outperforms the commercial catalyst Pt/C. The Ru@C₄N electrocatalyst also exhibits high HER turnover frequencies of 0.93 H₂ per s in 0.5 M H₂SO₄ and 0.65 H₂ per s in 1.0 M KOH solutions at 25 mV as well as superior performance stability.