Ru Nanoclusters Research Articles

Elucidating the role of confinement and shielding effect over zeolite enveloped Ru catalysts for propane low temperature degradation.

Volatile organic compounds (VOCs) are the main precursor for ozone formation and hazardous to human health. Light alkane as one of the typical VOCs is difficult to degrade to CO2 and H2O by catalytic degradation method due to its strong C-H bond. Herein, a series of ultrafine Ru nanoclusters (<0.95nm) enveloped in silicalite-1 (S-1) zeolite catalysts were designed and prepared by a simple one-pot method and applied for catalytic degradation of propane. The results demonstrate that the enveloped Ru1@S-1 catalyst has excellent propane degradation performance. Its T95 is as low as 294°C with moisture, and the turnover frequency (TOF) value is up to 5.07 × 10-3 s-1, evidently higher than that of the comparison supported catalyst (Ru1/S-1). Importantly, Ru1@S-1 exhibits superior thermal stability, water resistance and recyclability, which should be attributed to the confinement and shielding effect of the S-1 shell. The in-situ DRIFTS result reveals that the propane degradation over Ru1@S-1 follows the Mars-van-Krevelen (MvK) mechanism, where the hydroxy from the framework of zeolite can provide the active oxygen species. Our work provides a new candidate and guideline for an efficient and stable catalyst for the low-temperature degradation of the light alkane VOCs.

Coordination Engineering of Ultra‐Uniform Ruthenium Nanoclusters as Efficient Multifunctional Catalysts for Zinc–Air Batteries

The lack of highly efficient, inexpensive catalysts severely hinders the large‐scale application of electrochemical energy conversion technologies (e.g., electrochemical hydrogen evolution reaction (HER) for hydrogen production, metal–air batteries (Cathode: oxygen reduction reaction (ORR))). As a new class of nanomaterials with a high ratio of surface atoms and tunable composition and electronic structure, metal nanocluster (NCs) are promising candidates as catalysts. Herein, a novel catalyst using S,N‐doped carbon matrix (NSCSs) is synthesized to efficiently stabilize high density and ultra‐uniform ruthenium (Ru) nanoclusters (Ru@NSCSs) by small‐molecule self‐assembly pyrolysis approach. The obtained Ru@NSCSs catalyst exhibits outstanding HER activity in all pH conditions (especially with a low overpotential of 5 mV at a current density of 10 mA cm−2 in 1 m KOH) and excellent ORR performance (half‐wave potential (E 1/2) of 0.854 V in 0.1 m KOH). Based on the experimental investigations and theoretical calculations, it is discovered that the S‐atom can modulate the electronic structure and optimization of redox states on the surficial sites of Ru NCs during the ORR process. This work provides a feasible strategy for understanding and regulating the metal–support interface of ultra‐uniform nanoclusters catalysts.

An all-in-one zeolite@Ru–Al2O3 nanoplatform toward highly efficient, anti-coking, and recyclable hydrocarbon cracking catalysis

Efficient utilization of hydrocarbon fuels holds great significance for the current vehicle low-emission requirements and future carbon-neutral society. However, the scenario that limits the effective fuel use and combustion is the present undesirable hydrocarbon-cracking catalysts of low activity, serious coking, and easy degradation. To tackle these issues, we rationally designed and synthesized an active, anti-coking, and recyclable all-in-one zeolite@Ru–Al2O3 catalyst on FeCrAl support by steam-assisted crystallization and atomic layer deposition. Ru nanoclusters dispersedly on ZSM-5 can boost the catalytic efficiency for hydrocarbon cracking and anti-coking, while the protective Al2O3 thin layers further ensure the reusable economy. As for n-dodecane (C12H26) cracking reaction, the ZSM-5@Ru–Al2O3 showed a high unit activity up to 0.1253%·ml·mg−1·min−1, low-carbon deposition rate, and the enhanced first-cycle carbon removal rate of 78.3% for recyclable use. Density functional theory (DFT) calculations have further confirmed that high catalytic efficiency and low-carbon deposition benefit from the timely adsorption of C12H26 and timely transfer of reactant products at the composite interface. This work opens interesting possibilities for the rational design and fabrication of high-efficient, anti-coking, and recyclable hydrocarbon cracking catalysts through multifunctional structural regulations.

Turning CO2 to CH4 and CO over CeO2 and MCF-17 supported Pt, Ru and Rh nanoclusters – Influence of nanostructure morphology, supporting materials and operating conditions

Efficient conversion of CO2 into CH4 and CO brings an important opportunity to get valuable feedstock for a variety of industrially important reactions as both CH4 and CO are widely used as starting materials for the synthesis of valuable fuels and chemicals. Herein, we synthesized sub-nanometer (<2nm) Platinum (Pt), Ruthenium (Ru) and Rhodium (Rh) nanoclusters (NCs) via colloidal method; successfully decorated over mesoporous CeO2 and high surface area (HSA) siliceous meso-cellular foam (MCF 17) and tested for high-pressure CO2 reduction at lower temperature range (220–340 °C). Pt and Ru NCs exhibited typical reverse water gas shift (RWGS) and methanation catalytic performance respectively with minimal influence of the nature of support however, Rh NCs showed drastic variations in the product selectivity which exhibited strong influence of the support over the product distribution. Furthermore, Ru NCs (with a relatively lower metal loading ∼ 1 wt%) were found to be highly selective to CH4 (∼99 %) and stable (upto 40 hr time on stream) with either CeO2/MCF 17 at 340 °C; also Ru NCs exhibited comparatively the highest CO2 conversion (∼93 % in case of Ru NCs/CeO2) among the supported metal NCs. HRTEM results showed that metal NCs were homogeneously dispersed with a controlled and uniform particle size (<2nm); no substantial agglomeration of Ru NCs were observed after reaction. Beside the stable dispersion of NCs, Near Ambient Pressure (NAP) in situ XPS of Ru/CeO2 showed that the dynamic Ce3+/Ce4+ ratio of CeO2 can attribute to the high activity and selectivity.

Plasma-assisted highly dispersed Pt single atoms on Ru nanoclusters electrocatalyst for pH-universal hydrogen evolution

Exploring highly active and stable electrocatalyst using trace noble metals for hydrogen evolution reaction (HER) is urgently needed but still challenging. Here, atomically dispersed Pt on ultrafine Ru nanoclusters (∼1.46 nm) loaded by the commercial acetylene black (Acet) support is fabricated by a facile one-step cold-plasma technique. The Pt single atoms on Ru nanoclusters electrocatalyst (Pt0.47-Ru/Acet) with 0.47 wt% content of Pt exhibit an excellent HER activity in all pH, achieving ultralow overpotential of only 17, 28, and 8 mV at 10 mA·cm−2 in 1 M KOH, 0.5 M H2SO4, and 1 M PBS, respectively. And the mass activity of Pt0.47-Ru/Acet catalyst in alkaline is about 5.54 and 2.15 times that of commercial Ru/C and Pt/C catalyst at an overpotential of 100 mV, respectively. Meanwhile, after 8000 CV cycles, there is barely performance decrease for Pt0.47-Ru/Acet, displaying good stability. DFT calculation reveals that the Pt single atoms could effectively regulate the electronic structure of Ru clusters, and reduce the energy barriers of water dissociation (Volmer step) as well as subsequent hydrogen evolution (Heyrovsky step), thus enhancing the alkaline HER performance effectively. This work provides an effective approach to designing a high-performance HER electrocatalyst with the atomic-dimension Pt surface modification.

Adsorption and decomposition mechanism of N2O molecule over MC23 (M = Ru, Mn, V, Pd, and Rh) nanoclusters: A comparative DFT investigation

Adsorption and decomposition mechanism of N2O molecule over MC23 (M = Ru, Mn, V, Pd, and Rh) nanoclusters: A comparative DFT investigation

Front Cover Image: Volume 3 Issue 2

Front cover image: Ruthenium-based electrocatalysts have great potential as an alternative to platinum-based materials for the electrolysis of water for hydrogen evolution. In this work, a unique two-site mechanism of the ruthenium single/dual atoms and Ru nanoclusters to strengthen the stability of single atom sites and enhance its intrinsic activity was identified. Ru S/DAs and Ru NCs demonstrate high electroactivity due to the electroactive Ru 4d orbitals. The introduction of Ru NCs activates the carbon support, providing a high electronic conductivity to transfer electrons from Ru NCs to Ru S/DAs, and facilitates water dissociation for the HER process. (DOI: 10.1002/smm2.1067)

Synergistically boosting the elementary reactions over multiheterogeneous ordered macroporous Mo2C/NC‐Ru for highly efficient alkaline hydrogen evolution

AbstractSimultaneously enhancing the reaction kinetics, mass transport, and gas release during alkaline hydrogen evolution reaction (HER) is critical to minimizing the reaction polarization resistance, but remains a big challenge. Through rational design of a hierarchical multiheterogeneous three‐dimensionally (3D) ordered macroporous Mo2C‐embedded nitrogen‐doped carbon with ultrafine Ru nanoclusters anchored on its surface (OMS Mo2C/NC‐Ru), we realize both electronic and morphologic engineering of the catalyst to maximize the electrocatalysis performance. The formed Ru‐NC heterostructure shows regulative electronic states and optimized adsorption energy with the intermediate H*, and the Mo2C‐NC heterostructure accelerates the Volmer reaction due to the strong water dissociation ability as confirmed by theoretical calculations. Consequently, superior HER activity in alkaline solution with an extremely low overpotential of 15.5 mV at 10 mA cm−2 with the mass activity more than 17 times higher than that of the benchmark Pt/C, an ultrasmall Tafel slope of 22.7 mV dec−1, and excellent electrocatalytic durability were achieved, attributing to the enhanced mass transport and favorable gas release process endowed from the unique OMS Mo2C/NC‐Ru structure. By oxidizing OMS Mo2C/NC‐Ru into OMS MoO3‐RuO2 catalyst, it can also be applied as efficient oxygen evolution electrocatalyst, enabling the construction of a quasi‐symmetric electrolyzer for overall water splitting. Such a device's performance surpassed the state‐of‐the‐art Pt/C || RuO2 electrolyzer. This study provides instructive guidance for designing 3D‐ordered macroporous multicomponent catalysts for efficient catalytic applications.

Ordered mesoporous carbon spheres assisted Ru nanoclusters/RuO2 with redistribution of charge density for efficient CO2 methanation in a novel H2/CO2 fuel cell

Efficiently reducing carbon dioxide (CO2) into carbon chemicals and fuels is highly desirable due to the rapid growth of atmospheric CO2 concentration. In prior work, we described a unique H2/CO2 fuel cell driven by low-valued waste heat, which not only converts CO2 to methane (CH4) but also outputs electrical energy, yet the CO2 reduction rate needs to be urgently improved. Here, a novel Ru-RuO2 catalyst with heterostructure was grafted on mesoporous carbon spheres by in situ partially reducing RuO2 into ultrasmall Ru clusters (∼1 nm), in which heteroatom-doped carbon spheres as a matrix with excellent conductivity and abundant pores can not only easily confine the formation of Ru nanocluster but also are beneficial to the exposed active sites of Ru complex and the mass transport. Compared to pure RuO2 nanoparticles supported on carbon spheres, our composite catalyst boosts the CO2 conversion rate by more than 5-fold, reaching a value of 382.7 μmol gcat.-1h−1 at 170 ℃. Moreover, a decent output power density of 2.92 W m−2 was obtained from this H2/CO2 fuel cell using Ru-RuO2 embedded carbon spheres as a cathode catalyst. The Ru-RuO2 heterostructure can modify the adsorption energy of CO2 and induce the redistribution of charge density, thus boosting CO2 reduction significantly. This work not only offers an efficient catalyst for this novel H2/CO2 fuel cell but also presents a facile method to prepare Ru nanoclusters.

A one-pot carbon-coating-ex-solution route to efficient Ru-MnO@C nanowire electrocatalysts with enhanced interfacial interactions

The immobilization of metal nanoclusters in an inorganic matrix has attracted intense research interest because of its usefulness in exploring highly efficient electrocatalyst materials. In this study, a novel one-pot carbon-coating-ex-solution route to robust high-performance electrocatalysts of metal-nanocluster-embedded carbon-coated inorganic nanostructures was developed by the C2H2 treatment of metal-substituted MnO2 nanowires at elevated temperatures. The calcination of Ru-substituted Mn1-xRuxO2 nanowires under a flow of C2H2/Ar led not only to the simultaneous carbon coating and reductive formation of MnO, but also to the ex-solution embedding of Ru nanoclusters between the MnO substrate and the coated carbon layers. The resulting Ru-embedded Ru-MnO@C nanowires showed a promising electrocatalytic performance with an improved stability for the hydrogen evolution reaction (HER), and this performance was superior to those of Ru-deposited Ru-MnO@C nanowires, Ru-free MnO@C nanowires, and Mn1-xRuxO2 nanowires. The Ru-MnO@C nanowires possessed an excellent electrochemical stability due to the formation of strong interfacial Ru4+-O-Mn2+ bonding and the promoted crystallization of the tight graphitic carbon layer by Ru anchoring. Furthermore, in situ surface-enhanced Raman scattering and electron paramagnetic resonance analyses provided strong evidence for the improved interfacial charge transfer kinetics and enhanced electron injection from MnO to the Ru nanoclusters. This is responsible for the beneficial effect of the simultaneous carbon-coating-ex-solution process on the HER electrocatalyst functionality.

Insight into the critical role of strong interaction between Ru and Co in RuCo single-atom alloy structure for significant enhancement of ammonia synthesis performance

Rational design of efficient catalysts for ammonia (NH3) synthesis at mild conditions is of paramount importance for the development of electrolysis driven Haber-Bosch (eHB) process. Ammonia synthesis is a structure sensitive reaction, and any small change of electronic structure could result in dramatic change of catalytic activity, especially for the Ru-based NH3 synthesis catalysts. Electronic structure modulation of the Ru-based catalysts could provide desirable catalytic activity. Herein, we explore a class of Ru-Co single-atom alloy catalysts (marked as RuxCo1 SAA, x stands for Ru/Co molar ratio), in which Co single atoms are located on Ru nanoclusters to form Co-Ru coordination, and then electronic structure of RuxCo1 SAA could be effectively tuned by regulating the Ru/Co molar ratio. Our studies show that a moderate ratio of Ru/Co (1.7:1) favors superior NH3 synthesis rate and low activation energy. Using a suite of elaborate characterizations, we have observed that the outstanding performance over Ru1.7Co1 SAA can be attributed to the electron redistribution between Ru and Co atom, resulting in an upshift of d band center and lowering of work function. However, there is decrease of NH3 synthesis rate when Ru/Co molar ratio is 2, due to the partial detachment of Ru entities from SAA structure, and the formed individual Ru nanoparticles (NPs) overlay the surface of catalyst. In such a case, N2 activation behavior over Ru2Co1 is alike that of Ru NPs catalysts. The present study demonstrates that the Ru/Co ratio in SAA structure can effectively regulate the electronic structure of catalyst for NH3 synthesis rate enhancement.

Superassembly of Surface-Enriched Ru Nanoclusters from Trapping-Bonding Strategy for Efficient Hydrogen Evolution.

Hydrogen evolution reaction (HER) through water splitting is a potential technology to realize the sustainable production of hydrogen, yet the tardy water dissociation and costly Pt-based catalysts inhibit its development. Here, a trapping-bonding strategy is proposed to realize the superassembly of surface-enriched Ru nanoclusters on a phytic acid modified nitrogen-doped carbon framework (denoted as NCPO-Ru NCs). The modified framework has a high affinity to metal cations and can trap plenty of Ru ions. The trapped Ru ions are mainly distributed on the surface of the framework and can form Ru nanoclusters at 50 °C with the synergistic effect of vacancies and phosphate groups. By adjusting the content of phytic acid, surface-enriched Ru nanoclusters with adjustable distribution and densities can be obtained. Benefiting from the adequate exposure of the active sites and dense distribution of ultrasmall Ru nanoclusters, the obtained NCPO-Ru NCs catalyst can effectively drive HER in alkaline electrolytes and show an activity (at overpotential of 50 mV) about 14.3 and 9.6 times higher than that of commercial Ru/C and Pt/C catalysts, respectively. Furthermore, the great performance in solar to hydrogen generation through water splitting provides more flexibility for wide applications of NCPO-Ru NCs.

Crystalline Modulation Engineering of Ru Nanoclusters for Boosting Ammonia Electrosynthesis from Dinitrogen or Nitrate.

Developing highly efficient nitrogen reduction reaction (NRR) and nitrate reduction reaction (NITRR) electrocatalysts is an ongoing challenge. Herein, we report the in situ growth of ultrafine amorphous Ru nanoclusters with a uniform diameter of ∼1.2 nm on carbon nanotubes as a highly efficient electrocatalyst for both the NRR and the NITRR. The amorphous Ru nanoclusters were prepared via a convenient ambient chelated co-reduction method, in which trisodium citrate as a chelating agent played a key role to form amorphous Ru instead of crystalline Ru. The strong d-π interaction between Ru metal and carbon nanotubes led to the homogeneous distribution and good long-term stability of ultrafine Ru nanoclusters. Compared with crystalline Ru, amorphous Ru nanoclusters with abundant low-coordinate atoms can provide more catalytic sites. The amorphous Ru nanoclusters exhibited an NH3 yield of 10.49 μg·h-1·mgcat.-1 and a FENH3 of 17.48% at -0.2 V vs reversible hydrogen electrode (RHE) for NRR. For the NITRR, an NH3 yield of 145.1 μg·h-1·mgcat.-1 and a FENH3 of 80.62% were also achieved at -0.2 V vs RHE. This work provides new insights into crystalline modulation engineering of metal nanoclusters for electrocatalytic ammonia synthesis.

Strong electronic coupling between ruthenium single atoms and ultrafine nanoclusters enables economical and effective hydrogen production

Although Ru-based materials have been recognized as promising electrocatalysts for hydrogen evolution reaction (HER), further improving the mass activity and guaranteeing the high-throughput H2 production of the catalysts is of vital importance. Herein, Ru single atoms coupling with ultrafine nanoclusters on hierarchical porous N-doped carbon (NMC-RuSA+NC) has been synthesized as economical and effective HER catalysts. Density function theory and the experimental results reveal that the strong electronic coupling effects between Ru single atoms and nanoclusters and unique hierarchical structure enable NMC-RuSA+NC with the ultralow overpotential for achieving 500 mA cm−2 in alkaline and acidic conditions. More importantly, the NMC-RuSA+NC affords a higher mass activity and a lower cost for generating H2 than those of commercial Pt/C, justifiably proving its remarkable advantages for industrial use. This work offers precise guidance to design catalysts for high-throughput H2 production from the in-depth understanding of the electronic coupling effect of coupling active sites.

Well-dispersed ZIF-derived N-doped carbon nanoframes with anchored Ru nanoclusters as HER electrocatalysts

Nano-structuring and metal-support interactions are effective methods to improve the electrocatalytic activity of heterogeneous catalysis. In this study, we synthesized nitrogen-doped porous carbon substrates by using a SiO2-protected calcination strategy with ZIF-8 as a precursor. The experimental results revealed the prepared porous nitrogen-doped carbon (PNC) to have high dispersion, large specific surface area, and rich pore structure, allowing high exposure of active sites. The carbon support showed optimum characteristics to deposit precious metals with small particle sizes. X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) showed that the N groups on the PNC substrates served as coordination sites for Ru, allowing the formation of ultrafine nanoclusters. The Ru clusters showed good metal dispersion, exposing more active sites and improving the utilization of the precious metal. At a current density of 10 mA/cm2, Ru/PNC showed a minimum overpotential of 40 mV. This work provided a simple and effective method for the preparation of excellent carbon substrates and the synthesis of metal clusters with small particle sizes.

Amorphization of Metal Nanoparticles by 2D Twisted Polymer for Super Hydrogen Evolution Reaction (Adv. Energy Mater. 16/2022)

Hydrogen Evolution Reaction In article number 2102257 Hyoyoung Lee and co-workers report a novel strategy to synthesize amorphous metal nanoparticles with the help of a twisted covalent organic network. The prepared amorphous Ru nanocluster shows higher hydrogen generation reaction mass activity than commercial Pt/C with superior stability in alkaline conditions.

Facile MOF-derived one-pot synthetic approach toward Ru single atoms, nanoclusters, and nanoparticles dispersed on CeO2 supports for enhanced ammonia synthesis

The Haber-Bosch process for NH3 production is one of the largest global energy consumers. Despite improvements over the past century, developing catalysts with enhanced activities and durabilities remains challenging. Ru-based catalysts supported on CeO2 are suitable alternatives under mild reaction conditions. Here, we elucidated the effects of Ru structure on the physicochemical properties and catalytic activities of Ru-CeO2 systems. One-pot syntheses with metal–organic frameworks as sacrificial templates were used to prepare Ru single-atom, nanocluster, and nanoparticle systems. The Ru nanoclusters and single atoms exhibited superior and more stable performances toward NH3 production, with no hydrogen poisoning, in relation to the Ru nanoparticles. Kinetic data and electronic energy calculations demonstrated that the Ru nanoclusters coexisting with Ru single atoms may maximize the NH3 synthetic activity via the combination of dissociative and associative mechanisms. These results provide guidance for the rational design and optimization of Ru-based catalysts for use in NH3 synthesis.

Coupling of Ru nanoclusters decorated mixed-phase (1T and 2H) MoSe2 on biomass-derived carbon substrate for advanced hydrogen evolution reaction

The development of efficient catalysts for hydrogen evolution reaction (HER) from water splitting is one of the most promising strategies to achieve the goal of peak carbon dioxide emissions and carbon neutrality. Herein, Ru nanoclusters decorated MoSe2 nanosheets supported on a Crepis tectorum fluff biomass-derived hollow carbon tube (Ru-MoSe2/CMT) are prepared as the HER catalysts in both alkaline and acidic conditions. The Ru modification induces the transformation of MoSe2 from 2H phase to 1T phase. Benefiting from the strong water dissociation ability of Ru, Ru-MoSe2/CMT exhibits a low overpotential of 70 mV with a Tafel slope of 39 mV dec-1 in 1 M KOH. Furthermore, the assembled Ru-MoSe2/CMT || RuO2 system with a low cell voltage of 1.54 V at 10 mA cm−2 exhibits outstanding overall water splitting performance superior to Pt/C || RuO2 system. The Ru-MoSe2/CMT || RuO2 system also achieves the excellent stability of up to 30 h in 1 M KOH. The synergy effect between Ru and MoSe2, as well as the improved electron transfer kinetics provided by the biomass-derived carbon substrate together contribute to the excellent HER activity of Ru-MoSe2/CMT.

Size-dependent activity of supported Ru catalysts for ammonia synthesis at mild conditions

Ammonia (NH3) synthesis is a structure-sensitive reaction, where a minute variation of catalyst structure would lead to a dramatic change of activity. To date, the roles of Ru size on NH3 synthesis still remain elusive, and it remains a major challenge. Herein, a series of Ru catalysts with sizes ranging from 1.4 to 5.0 nm were prepared by colloidal Ru deposition, which allows the investigation of size influence on NH3 synthesis. Through analyses of the geometric and electronic properties of variable-sized Ru particles, it shows that the reduction of Ru particle size could increase the proportion of corner sites while decrease that of terrace sites, which can decrease the work function and thus promote N2 for its activation. Isotopic investigations show that the decrease of dissociative contribution but the increase of associative contribution as Ru particle size was decreased from 5.0 to 1.4 nm. Meanwhile, the NH3 synthesis rate increases when the size of Ru catalysts decreases from 5.0 to 1.4 nm. Using a suite of elaborate characterizations, we have observed that 1.4 nm Ru nanoclusters (NCs) with ample corner sites are conducive to activate N2 via an associative route. As a result, the 1.4 nm Ru NCs catalyst shows the highest NH3 synthesis rate (up to 17.13 mmolNH3 gcat−1h−1) at 400 ℃ and 1 MPa.

Ru-incorporated oxygen-vacancy-enriched MoO2 electrocatalysts for hydrogen evolution reaction

Designing highly efficient Pt-free electrocatalysts with low overpotential for the alkaline hydrogen evolution reaction (HER) remains a significant challenge. In this paper, we successfully construct Ru-incorporated oxygen-vacancy-enriched MoO2 nanosheets (Ru/MoO2−x) for the HER through a “one stone two birds” strategy. This strategy can solve two urgent problems simultaneously, the intrinsic electrochemical activity of original MoO2 is far from satisfactory and the H2O adsorption/dissociation abilities of Ru are weak. Specifically, the oxygen-vacancy-enriched MoO3 serves as an excellent platform for anchoring and trapping Ru ions. In-depth analyses indicate that the incorporation of Ru nanoclusters induces transition from MoO3 to MoO2, generates oxygen vacancies, and creates Ru-O-Mo sites. The synergistic effect of Ru nanoclusters, Ru-O-Mo sites and oxygen-vacancy-enriched MoO2 will endow the obtained catalyst excellent electrocatalytic activity. In particular, the optimal Ru/MoO2−x electrocatalyst delivered a low overpotential of 29 mV at 10 mA cm−2 in a basic electrolyte.