Volmer-Tafel Mechanism Research Articles

Highly porous Pt3Ni nanosheets for enhanced hydrogen evolution reaction

Two-dimensional (2D) nanosheets with high surface-to-volume ratios have garnered significant attention for their electrocatalytic properties. This study explores the characterization and electrocatalytic performance of highly porous monometallic platinum (Pt) nanosheets and bimetallic platinum-nickel (Pt3Ni) nanosheets for the hydrogen evolution reaction (HER) in both alkaline and acidic media. Advanced characterization techniques were employed to elucidate the morphological and compositional properties of the Pt and Pt3Ni nanosheets. Electrochemical characterization demonstrated that Pt3Ni nanosheets/C outperformed Pt nanosheets/C and commercial Pt/C in terms of HER activity and stability. The enhanced HER performance of Pt3Ni nanosheets/C is believed to be due to the dominance of the Volmer-Tafel mechanism. These findings highlight the potential of 2D bimetallic nanosheets and suggest a promising avenue for advancing hydrogen energy technologies.

High Entropy Alloys as High Performance Catalysts for Electrolytic Water Splitting

Renewable energy driven electrolytic water splitting is a required technology for low-carbon hydrogen production to achieve the goal of net-zero CO2 emission by 2050. This technology also serves as a necessary energy storage route to resolve the intolerable intermittency and unreliability issues of renewable energies. The prevailing of this hydrogen production technology however is restricted by the high cost of electricity. Consequently, developments of cost–effective highly efficient and stable electrocatalysts to drive the electrolytic water splitting reactions are the key. In terms of catalyst developments, mono-component systems are first explored, followed by multi–component systems, taking advantages of possible positive synergy between constituent components. Recently, a new class of multi-component catalyst systems, entropy-stabilized materials, including alloys, oxides, sulfides, phosphides, etc., emerges and is demonstrated promising performances toward electrocatalysis. In light of the variable and flexible element compositions, entropy-stabilized materials provide infinite and enormous potentials for the design of promising electrocatalysts. The key is to maximize the synergy between constituent components. High entropy alloys (HEA), defined as alloys composed of five or more major metallic elements, have been under intensive and extensive development in past fifteen years for their extraordinary mechanical, magnetic, corrosion, and catalytic properties. Herein, an equi–molar FeCoNiCuMo HEA on nickel foam was developed as a breakthrough catalyst for electrocatalytic water splitting, in terms of both activity and stability, in pH-universal media and in severe industrial operation conditions. Furthermore, a new catalytic phenomenon is discovered. Two different catalytic mechanisms function simultaneously on different constituents of the catalyst, and the synergistic interactions between the two categorical domains leads to catalytic kinetics faster than the theoretical limit set by a single rate-limiting step, Tafel step of the Volmer-Tafel route. A new kinetic model is developed to predict a new theoretical lower limit of Tafel slopes of 15 mV/dec based on a synergistic interaction between the two categorical domains of the high entropy alloy catalyst. This new development proves that the theoretical lower limit of Tafel slope of 30 mV/dec posed for the Volmer-Tafel mechanism functioning on a single component catalyst can be further reduced to 15 mV/dec through synergistic interactions between two categorical domains of a multi-component catalyst. It is demonstrated that high entropy materials, composed of five or more atomically/molecularly well-mixed major components, are intrinsically promising candidates for realization of quantum leaps in catalytic performances of catalysts.

Electrocatalytic Performance of 2D Monolayer WSeTe Janus Transition Metal Dichalcogenide for Highly Efficient H2 Evolution Reaction.

Nowadays, the development of clean and green energy sources is the priority interest of research due to increasing global energy demand and extensive usage of fossil fuels, which create pollutants. Hydrogen has the highest energy density by weight among all chemical fuels. For the commercial-scale production of hydrogen, water electrolysis is the best method, which requires an efficient, cost-effective, and earth-abundant electrocatalyst. Recent studies have shown that the 2D Janus transition metal dichalcogenides (JTMDs) are promising materials for use as electrocatalysts and are highly effective for electrocatalytic H2 evolution reaction (HER). Here, we report a 2D monolayer WSeTe JTMD, which is highly effective toward HER. We have studied the electronic properties of 2D monolayer WSeTe JTMD using the periodic hybrid DFT-D method, and a direct electronic band gap of 2.39 eV was obtained. We have explored the HER pathways, mechanisms, and intermediates, including various transition state (TS) structures (Volmer TS, i.e., H*-migration TS, Heyrovsky TS, and Tafel TS) using a molecular cluster model of the subject JTMD noted as W10Se9Te12. The present calculations reveal that the 2D monolayer WSeTe JTMD is a potential electrocatalyst for HER. It has the lowest energy barriers for all the TSs among other TMDs. It has been shown that the Heyrovsky energy barrier (= 8.72 kcal mol-1) in the case of the Volmer-Heyrovsky mechanism is larger than the Tafel energy barrier (= 3.27 kcal mol-1) in the Volmer-Tafel mechanism. Hence, our present study suggests that the formation of H2 is energetically more favorable via the Volmer-Tafel mechanism. This study helps to shed light on the rational design of 2D single-layer JTMD, which is highly effective toward HER, and we expect that the present work can be further extended to other JTMDs to find out the improved electrocatalytic performance.

Ultrahigh Pt-mass-activity catalyst for alkaline hydrogen evolution synthesized by microwave method in air

Platinum (Pt) metal is widely acknowledged as a highly efficient electrocatalyst for hydrogen evolution reaction (HER) in acidic electrolyte. However, its performance in alkaline environments is significantly lower owing to the sluggish water dissociation step. Herein, we synthesized an ultrahigh Pt-mass-activity alkaline HER catalyst using microwave reduction method in air. Our catalyst, PtRu@CNT, comprises PtRu alloy nanoparticles uniformly loaded on carbon nanotubes, with Pt and Ru contents of 12.3 wt% and 4.5 wt%, respectively. The PtRu alloy nanoparticles have an average diameter of about 3 nm and a face-centered cubic structure, and the introduction of Ru has led to a modified electronic structure in Pt. As a result, an impressively low HER overpotential of 13 mV was achieved, significantly lower than commercial 20 wt% Pt/C (61 mV). PtRu@CNT exhibited a high turnover frequency based on metal mass of 3.06 s−1 at 100 mV, about 6 times higher than commercial Pt/C (0.46 s−1 at 100 mV), highlighting its excellent intrinsic activity. The HER mechanism of PtRu@CNT is a Volmer-Tafel mechanism, where the rate-limiting step changed to the recombination of hydrogen atoms from initial water dissociation, attributed to the presence of Ru. The alkaline HER activity of PtRu@CNT ranks among the best of currently reported Pt-based catalysts.

Strong Metal-Support Interaction Modulation between Pt Nanoclusters and Mn3O4 Nanosheets through Oxygen Vacancy Control to Achieve High Activities for Acidic Hydrogen Evolution.

The optimization of metal-support interactions is used to fabricate noble metal-based nanoclusters with high activity for hydrogen evolution reaction (HER) in acid media. Specifically, the oxygen-defective Mn3O4 nanosheets supported Pt nanoclusters of ≈1.71nm in diameter (Pt/V·-Mn3O4 NSs) are synthesized through the controlled solvothermal reaction. The Pt/V·-Mn3O4 NSs show a superior activity and excellent stability for the HER in the acidic media. They only require an overpotential of 19mV to drive -10mAcm-2 and show negligible activity loss at -10 and -250mAcm-2 for >200 and >60h, respectively. Their Pt mass activity is 12.4 times higher than that of the Pt/C and even higher than those of many single-atom based Pt catalysts. DFT calculations show that their high HER activity arises mainly from the strong metal-support interaction between Pt and Mn3O4. It can facilitate the charge transfer from Mn3O4 to Pt, optimizing the H adsorption on the catalyst surface and promoting the evolution of H2 through the Volmer-Tafel mechanism. The oxygen vacancies in the V·-Mn3O4 NSs are found to be inconducive to the high activity of the Pt/V·-Mn3O4 NSs, highlighting the great importance to reduce the vacancy levels in V·-Mn3O4 NSs.

Crucial Role of Metal Coordination Number in Optimizing Electrocatalyst Activity of Holey Large-Area 2D Ru Nanosheets.

Low-dimensional metal nanostructures have attracted considerable research attention, owing to their potential as catalysts. A controlled reductive phase transition of monolayer RuO2 nanosheets could provide an effective way to produce holey large-area 2D Ru nanosheets with tailored defect structures and metal coordination number. The locally optimized holey Ru metal nanosheet, with a metal coordination number of ∼10.2, exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) with a reduced overpotential of 38 mV in a 1 M KOH electrolyte. The creation of a highly anisotropic holey nanosheet morphology with optimization of local structure was quite effective in developing efficient catalyst materials. The universal importance of controlling the coordination number was confirmed through a comparative study of Ru nanoparticles, which showed optimized HER activity with an identical metal coordination number. The coordination number plays a pivotal role in governing electrocatalytic activity, which could be ascribed to the formation of the most active structure for HER at most 2 defects near active sites (2,2'), resulting in the stabilization of a dihydrogen Ru-(H2) intermediate and the increased contribution of Volmer-Tafel mechanism.

Mechanism of Electrocatalytic H2 Evolution, Carbonyl Hydrogenation, and Carbon-Carbon Coupling on Cu.

Aqueous-phase electrocatalytic hydrogenation of benzaldehyde on Cu leads not only to benzyl alcohol (the carbonyl hydrogenation product), but Cu also catalyzes carbon-carbon coupling to hydrobenzoin. In the absence of an organic substrate, H2 evolution proceeds via the Volmer-Tafel mechanism on Cu/C, with the Tafel step being rate-determining. In the presence of benzaldehyde, the catalyst surface is primarily covered with the organic substrate, while H* coverage is low. Mechanistically, the first H addition to the carbonyl O of an adsorbed benzaldehyde molecule leads to a surface-bound hydroxy intermediate. The hydroxy intermediate then undergoes a second and rate-determining H addition to its α-C to form benzyl alcohol. The H additions occur predominantly via the proton-coupled electron transfer mechanism. In a parallel reaction, the radical α-C of the hydroxy intermediate attacks the electrophilic carbonyl C of a physisorbed benzaldehyde molecule to form the C-C bond, which is rate-determining. The C-C coupling is accompanied by the protonation of the formed alkoxy radical intermediate, coupled with electron transfer from the surface of Cu, to form hydrobenzoin.

Spin Polarization of 2D Weyl Semimetal Fe2Sn Enabling High Hydrogen Evolution Reaction Activity.

It is well known that magnetic field is one of the effective tools to improve the activity of hydrogen evolution reaction (HER), but considering the inconvenient application of an external magnetic field, it is essential to find a ferromagnetic material with high HER activity itself. Fortunately, recent study has shown that the two-dimmention (2D) Fe2Sn monolayer is a stable ferromagnetic topological Weyl semimetal material with high Tc of 433 K. Here, we report the Fe2Sn monolayer can be used as an alternative HER catalyst compared with expensive platinum (Pt). Our first-principles results show that the Gibbs free energy (ΔGH*) value of the spin polarized Fe2Sn monolayer is -0.06 eV, much better than that without considering spin polarization (-1.23 eV). Moreover, the kinetic analysis demonstrates that the HER occurs on the Fe2Sn monolayer according to the Volmer-Tafel mechanism with low energy barriers. Hence, our findings provide obvious evidence for spin-polarization-improved HER activity, paving a new way to design high-performance HER catalysts.

Boosted hydrogen evolution kinetics of heteroatom-doped carbons with isolated Zn as an accelerant

Carbon-based single-atom catalysts, a promising candidate in electrocatalysis, offer insights into electron-donating effects of metal center on adjacent atoms. Herein, we present a practical strategy to rationally design a model catalyst with a single zinc (Zn) atom coordinated with nitrogen and sulfur atoms in a multilevel carbon matrix. The Zn site exhibits an atomic interface configuration of ZnN4S1, where Zn's electron injection effect enables thermal-neutral hydrogen adsorption on neighboring atoms, pushing the activity boundaries of carbon electrocatalysts toward electrochemical hydrogen evolution to an unprecedented level. Experimental and theoretical analyses confirm the low-barrier Volmer-Tafel mechanism of proton reduction, while the multishell hollow structures facilitate the hydrogen evolution even at high current intensities. This work provides insights for understanding the actual active species during hydrogen evolution reaction and paves the way for designing high-performance electrocatalysts.

Switch Volmer-Heyrovsky to Volmer-Tafel Pathway for Efficient Acidic Electrocatalytic Hydrogen Evolution by Correlating Pt Single Atoms with Clusters.

As cost-effective catalysts, platinum (Pt) single-atom catalysts (SACs) have attracted substantial attention. However, most studies indicate that Pt SACs in acidic hydrogen evolution reaction (HER) follow the slow Volmer-Heyrovsky (VH) mechanism instead of the fast kinetic Volmer-Tafel (VT) pathway. Here, this work propose that the VH mechanism in Pt SACs can be switched to the faster VT pathway for efficient HER by correlating Pt single atoms (SAs) with Pt clusters (Cs). Ourcalculations reveal that the correlation between Pt SAs and Cs significantly impacts the electronic structure of exposed Pt atoms, lowering the adsorption barrier for atomic hydrogen and enabling a faster VT mechanism. To validate these findings, this work purposely synthesize three catalysts: l-Pt@MoS2, m-Pt@MoS2 and h-Pt@MoS2 with low, moderate, and high Pt-loading, having different distributions of Pt SAs and Cs. The m-Pt@MoS2 catalyst with properly correlating Pt SAs and Cs exhibits outstanding performance with an overpotential of 47mV and Tafel slope of 32mV dec-1. Further analysis of the Tafel values confirms that the m-Pt@MoS2 sample indeed follows the VT reaction mechanism, aligning with the theoretical findings. This study offers a deep understanding of the synergistic mechanism, paving a way for designing novel-advanced catalysts.

Strategically Designed Pd-Induced Changes in Alkaline Hydrogen Evolution Reaction and Oxygen Evolution Reaction Performances of Electrochemical Water Oxidation by the Galvanically Synthesized MoO2/MoO3 Composite Thin Film.

Electrochemical water oxidation is believed to be an effective pathway to produce clean, carbon-free, and environmentally sustainable green energy. In this work, we report a simple, easy-to-construct, facile, low-cost, and single-step galvanic technique to synthesize a Pd-supported temperature-assisted MoOx thin film nanocomposite for effective water oxidation. The most suitable nanocomposite exhibits very low overpotential at 10 mA/cm2 with smaller Tafel slope values for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) processes in an alkaline medium. The formation of a metal oxide-metal junction accelerates the growth of more active sites, promoting induced electronic synergism at the MoOx-Pd interface. This endows higher electrical conductivity and faster electron transfer kinetics, thus accelerating the faster water dissociation reaction following the Tafel-Volmer mechanism to boost the HER process in an alkaline medium. The excellent electrochemical HER and OER performances of our electrocatalyst even supersede the accomplishments of the benchmark catalysts Pt/C and RuO2. Moreover, neither of these two catalysts demonstrates both catalytic reactions, i.e., HER and OER at the same time, which have been observed for our synthesized catalyst. Our findings illustrate the potential of a thin-film MoOx-Pd nanocomposite to be an exceedingly effective electrocatalyst developed by interface engineering strategies. This also provides insight into designing several other semiconductor composite catalysts using simple synthesis techniques for highly efficient HER/OER processes that could be alternatives to benchmark electrocatalysts for water electrolysis.

Platinum monolayer dispersed on MXenes for electrocatalyzed hydrogen evolution: a first-principles study.

Maximizing platinum's atomic utilization and understanding the anchoring mechanism between platinum moieties and their supports are crucial for the hydrogen evolution reaction (HER). Using density functional theory, we investigate the catalyst of a Pt monolayer on the two-dimensional Mo2TiC2 substrate (PtML/Mo2TiC2) for the reaction. This Pt monolayer shows a Pt(111)-like pattern, with its Pt-Pt bond elongated by about 0.1 Å compared to Pt(111); charge transfer from Mo2TiC2 to the Pt monolayer leads to significant charge accumulation on Pt. This substantial monolayer metal-support interaction optimizes hydrogen adsorption toward optimal HER activity under both constant charge and potential conditions, making PtML/Mo2TiC2 a promising HER catalyst. Detailed studies reveal that the dominant Volmer-Tafel mechanism in the HER occurs on the 1 monolayer hydrogen-covered PtML/Mo2TiC2 surface. The surface Pourbaix diagram identifies this as the stable surface termination under the electrochemical reaction conditions. These findings provide insights into designing stable, efficient, and low platinum-loaded HER catalysts.

Theoretical design of active Ga2O3 monolayer-based catalysts for electrocatalytic HER.

Electrocatalytic hydrogen evolution reaction (HER) offers a sustainable and clean route for hydrogen production. Developing a high-efficiency HER catalyst is extremely essential toward meeting future energy needs. Herein, the Sn-doped Ga2O3 monolayer, O-defected Ga2O3 monolayer, and Ru-adsorbed Ga2O3 monolayer with high electrocatalytic performances toward HER are reported (their H adsorption free energies are 0.169, 0.126 and 0.065 eV, respectively). The Sn-doped Ga2O3 monolayer follows the Volmer-Heyrovsky mechanism, and the O-defected Ga2O3 monolayer and Ru-adsorbed Ga2O3 monolayer are suitable for Volmer-Tafel mechanisms. The strain from -4% to 4% in the X- or Y-direction could linearly modulate the HER activities of the Sn-doped Ga2O3 monolayer and O-defected Ga2O3 monolayer. The Sn-doped Ga2O3 monolayer, O-defected Ga2O3 monolayer, and Ru-adsorbed Ga2O3 monolayer only manifest high HER catalytic activities in the strong acidic media. These phenomena can provide a rational approach to enhance the HER activity for Ga2O3 monolayer-based materials.

High efficient alkaline hydrogen evolution catalyzed by W2COx-Ru composite system containing bridged oxygen

The design of low-cost and high-performance hydrogen evolution reaction (HER) catalysts with small overpotentials under alkaline conditions to replace the high-cost platinum catalysts still faces obstacles. Here, we report a two-component catalytic system consisting of Ru-clusters supported on oxyanion-terminated W2COx, which makes it possible to generate unusual hydrogen under alkaline conditions by the kinetically fast Volmer-Tafel mechanism. The principal characteristic of the catalyst is that the two components are interconnected by an O bridge, which is used for rapid adsorption of the hydrogen intermediate generated during water dissociation and transfer it to W2COx. Because of this unique interface environment, the relayed H* combines and desorbs directly on the W2COx, creating the H2 through an unusual route of Tafel. The bridging O in the catalyst acts as a reversible adsorption and transport intermediate for H*, assuring the magnificent and sustainable HER performance of the material.

Theoretical study of the mechanism of the hydrogen evolution reaction on the V2C MXene: Thermodynamic and kinetic aspects

Both experimentally and theoretically, the MXene family has shown promising hydrogen evolution reaction (HER) capabilities. However, so far, the theoretical approach has been relying on the well-known thermodynamic descriptor, ΔGH, whereas experimental studies report Tafel plots, containing kinetic rather than thermodynamic information. Aiming to link theory to experiments, the present study explores five different HER pathways over the exemplary V2C (0001) MXene by density functional theory calculations. While the surface coverage under HER conditions (with either H* or OH* adsorbates) is extracted from a Pourbaix diagram, we determine the energetics of the reaction intermediates and transition states for both surface species as active sites. This enables the construction of free-energy diagrams for the Volmer-Heyrovsky and Volmer-Tafel mechanisms and allows for the simulation of Tafel plots by a rigorous microkinetic framework. While the active-site motif V2C-OH seems to be less relevant for the HER under typical reaction conditions, we demonstrate that the HER is kinetically facile on the V2C-H surface. For this surface termination, we report a potential-depending switching of the preferred mechanism from the Volmer-Heyrovsky to the Volmer-Tafel description with increasing overpotential while encountering similarities to the HER over Pt.

Development of metal-organic framework-derived NiMo-MoO3−x porous nanorod for efficient electrocatalytic hydrogen evolution reactions

In this study, we developed a noble metal-free HER electrocatalyst NiMo-MoO3−x porous nanorod (NiMo-MoO3−x −PNR) by optimal thermal reduction of NiMoO4 porous nanorod (NiMoO4 −PNR), where the porous structure of NiMoO4 −PNR was enabled by calcining the designed Ni-Mo-metal-organic framework nanorod (Ni-Mo-MOF−NR). As a result of its ideal porous nanorod structure, composition, and improved bifunctional properties, the electrocatalyst demonstrated superior HER performance (a low overpotential of 24.5 mV @ 10.0 mA cm−2) in 1 м KOH, which was comparable with that of state-of-the-art platinum group metals (PGMs) based electrocatalysts. Furthermore, NiMo-MoO3−x −PNR displayed faster Volmer-Tafel mechanism (a small Tafel slope of 32 mV dec−1) for HER process. The superior HER activity of NiMo-MoO3−x −PNR was supported by density functional theory simulations. Moreover, it exhibited a high cyclic stability (unaffected after 100,000 cycles) and robust durability (102 h). Overall, this study demonstrates a simple, scalable, and versatile synthesis of a noble metal-free highly efficient inexpensive electrocatalyst for HER.

Theoretical study of electrocatalytic properties of low-dimensional freestanding PbTiO3 for hydrogen evolution reactions.

The discovery of novel materials for catalytic purposes that are highly stable is one of the main challenges nowadays for reducing our dependence on fossil fuels. Here, low-dimensional PbTiO3 is introduced as an electrocatalyst using first-principles calculations. Density-functional theory calculations indicate that 2D-PbTiO3 is dynamically and thermodynamically stable. Our results show that a single oxygen defect vacancy in 2D-PbTiO3 can play a key role in enhancing the hydrogen evolution reaction (HER), together with the Ti atoms. Our study concludes that the Volmer-Heyrovsky mechanism is a more favorable route to achieve HER than the Volmer-Tafel mechanism, including solvation and vacuum conditions.

Enhanced alkaline hydrogen oxidation reaction using electrodeposited Ni-Ir alloy catalysts

The development of high-performance non/less-precious metal-based electrocatalysts for the hydrogen oxidation reaction (HOR) in anion exchange membrane fuel cells remains a challenge. Here, we report a bimetallic Ni-Ir catalyst fabricated using electrodeposition and optimized to improve its HOR performance in an alkaline environment. Bimetallic Ni-Ir catalysts of various compositions are electrochemically deposited on a glassy carbon (GC) disk electrode and their HOR activity in 0.1 M KOH is examined. It is found that Ni47Ir53 has the highest HOR activity of 2.09 and 2.28 mA cm−2 at 0.05 and 0.10 VRHE, respectively, outperforming a commercial Pt/C electrode. This improved performance is ascribed to the larger electrochemical surface area and the modification to the electronic structure via alloying. Electrochemical analysis revealed a low Tafel slope and a large exchange current density for Ni47Ir53, suggesting the presence of the Tafel-Volmer mechanism and a rapid Volmer reaction. The balanced H binding and OH binding with Ni47Ir53 is a significant contributor to the higher HOR activity. During accelerated durability testing, the oxidation state and electronic structure of the catalyst become more unfavorable for the HOR due to Ni dissolution, which supports the strategy of employing a dissolution-resistive alloying metal with Ir for alkaline HOR catalysts.

Alkali metal cations change the hydrogen evolution reaction mechanisms at Pt electrodes in alkaline media

The effects of seemingly inert alkali metal (AM) cations on the electrocatalytic activity of electrode materials towards reactions essential for energy provision have become the emphasis of substantial research efforts in recent years. The hydrogen and oxygen evolution reactions during alkaline water electrolysis and the oxygen electro-reduction taking place in fuel cells are of particular importance. There is no universal theory explaining all the details of the AM cation effect in electrocatalysis. For example, it remains unclear how “spectator” AM-cations can change the kinetics of electrocatalytic reactions often more significantly than the modifications of the electrode structure and composition. This situation originates partly from a lack of systematic experimental and theoretical studies of this phenomenon. The present work exploits impedance spectroscopy to investigate the influence of the AM cations on the mechanism of the hydrogen evolution reaction at Pt microelectrodes. The activity follows the trend: Li + ≥Na + >K + >Cs + , where the highest activity corresponds to 0.1 ​M LiOH electrolytes at low overpotentials. We demonstrate that the nature of the AM cations also changes the relative contribution of the Volmer–Heyrovsky and Volmer–Tafel mechanisms to the overall reaction, with the former being more important for LiOH electrolytes. Our density functional theory-based thermodynamics and molecular dynamics calculations support these findings.

Atomically Thin Holey Two-Dimensional Ru2P Nanosheets for Enhanced Hydrogen Evolution Electrocatalysis

The defect engineering of low-dimensional nanostructured materials has led to increased scientific efforts owing to their high efficiency concerning high-performance electrocatalysts that play a crucial role in renewable energy technologies. Herein, we report an efficient methodology for fabricating atomically thin, holey metal-phosphide nanosheets with excellent electrocatalyst functionality. Two-dimensional, subnanometer-thick, holey Ru2P nanosheets containing crystal defects were synthesized via the phosphidation of monolayer RuO2 nanosheets. Holey Ru2P nanosheets exhibited superior electrocatalytic activity for the hydrogen evolution reaction (HER) compared to that exhibited by nonholey Ru2P nanoparticles. Further, holey Ru2P nanosheets exhibited overpotentials of 17 and 26 mV in acidic and alkaline electrolytes, respectively. Thus, they are among the best-performing Ru-P-based HER catalysts reported to date. In situ spectroscopic investigations indicated that the holey nanosheet morphology enhanced the accumulation of surface hydrogen through the adsorption of protons and/or water, resulting in an increased contribution of the Volmer-Tafel mechanism toward the exceptional HER activity of these ultrathin electrocatalysts.