Electrocatalysts For Alkaline Hydrogen Evolution Reaction Research Articles

Lattice‐Matched Ru/W2C Heterointerfaces with Reversible Hydrogen Spillover for Efficient Alkaline Hydrogen Evolution

AbstractThe effect of lattice‐matched heterointerfaces on the hydrogen reverse spillover process for accelerating alkaline hydrogen evolution reaction (HER) kinetics has not yet been reported. Herein, a lattice‐matched Ru/W2C heterostructure is successfully constructed for effective hydrogen production. Experimental and theoretical results reveal that the Ru nanocluster can effectively stabilize W2C and thus promote the formation of phase‐pure W2C in the Ru/W2C heterostructure. In addition, it is revealed that H2O dissociation proceeded on W2C, and the formed H intermediates are subsequently migrated to adjacent interfacial Ru sites for H─H coupling and H2 release. This is enabled via a reversible hydrogen spillover mechanism promoted by the lattice‐matched heterointerfaces that can weaken interfacial proton adsorption. As expected, the Ru/W2C heterogeneous electrocatalyst exhibited a superior HER performance with a low overpotential of 17 mV at 10 mA cm−2, a high mass current density (6.44 A mgRu−1), and a low turnover frequency (TOF) value (2.8 s−1) at the overpotential of 100 mV, far overwhelming the benchmark Ru/C and Pt/C. The study may offer a new perspective for the design of highly active electrocatalysts for alkaline HER.

Alkaline Hydrogen Evolution Reaction Electrocatalysts for Anion Exchange Membrane Water Electrolyzers: Progress and Perspective.

For the aim of achieving the carbon-free energy scenario, green hydrogen (H2) with non-CO2 emission and high energy density is regarded as a potential alternative to traditional fossil fuels. Over the last decades, significant breakthroughs have been realized on the alkaline hydrogen evolution reaction (HER), which is a fundamental advancement and efficient process to generate high-purity H2 in the laboratory. Based on this, the development of the practical industry-oriented anion exchange membrane water electrolyzer (AEMWE) is on the rise, showing competitiveness with the incumbent megawatt-scale H2 production technologies. Still, great challenges lie in exploring the electrocatalysts with remarkable activity and stability for alkaline HER, as well as bridging the gap of performance difference between the three-electrode cell and AEMWE devices. In this perspective, we systematically discuss the in-depth mechanisms for activating alkaline HER electrocatalysts, including electronic modification, defect construction, morphology control, synergistic function, field effect, etc. In addition, the current status of AEMWE is reviewed, and the underlying bottlenecks that impede the application of HER electrocatalysts in AEMWE are summarized. Finally, we share our thoughts regarding the future development directions of electrocatalysts toward both alkaline HER and AEMWE, in the hope of advancing the commercialization of water electrolysis technology for green H2 production.

Constructing Ru-Co2P Lewis Acid-Base Pairs to Prompt Hydrogen Evolution Reaction in Alkaline Seawater Electrolyte.

Seawater electrolysis is an ideal approach to generating green hydrogen. Nevertheless, the sluggish kinetics of water dissociation and the detrimental chlorine chemistry environment are serious obstructions for industrial applications. Herein, constructing unique (Co) Lewis acid and (Ru-P) base pair sites in Ru-Co2P decorated on nitrogen and phosphorus co-doped carbon (Ru-Co2P/NPC) significantly optimizes the energy barrier of water dissociation and enhances the anti-corrosive ability for alkaline seawater splitting. As expected, the optimal Ru-Co2P/NPC-2 exhibits exceptional hydrogen evolution reaction (HER) performances with overpotentials as low as 22.0 and 26.0mV to derive 10 mAcm-2 and operate steadily (@ 50 mAcm-2) over 30 h in alkaline and alkaline seawater electrolytes. The experimental and theoretical results elucidate that Co acting as Lewis acid sites prompts the water adsorption and breakage of the H─O bond, whereas Ru-P as Lewis base sites facilitates the hydrogen desorption in alkaline media. Furthermore, modulated chemical microenvironments can be beneficial to hinder chloride corrosion on the active sites of catalysts. This work sheds light on the rational construction of a highly efficient electrocatalyst for alkaline HER in seawater.

Sustainable hydrogen production with synergistic electron transfer enhancement in nickel-based alkaline HER electrocatalyst empowered by graphene oxide

The hydrogen evolution reaction (HER) plays a crucial role in driving forward the transition to a hydrogen-based economy by providing a means to generate pure hydrogen. However, the efficient and cost-effective production of hydrogen via HER faces significant challenges, particularly at the cathode. To address these challenges, we produced a hybrid material – 2D graphene oxide (GO) sheets coated onto nickel sulfide (NiS) microspheres anchored on Ni Foam (GO@NiS/Ni Foam) using a straightforward synthesis technique. Our research highlights the significant influence of the interaction between GO and NiS on the performance of HER, attributed to the enhancement of electron transport at the interface. Furthermore, the GO@NiS/Ni Foam composite exhibits remarkable durability over extended periods, maintaining its superior functionality for up to 40 h of continuous operation. This underscores its potential for practical implementation in efficient water-splitting processes, offering a promising solution to the challenges hindering widespread adoption of hydrogen technology.

Rationally Designed Mo/Ru-Based Multi-Site Heterogeneous Electrocatalyst for Accelerated Alkaline Hydrogen Evolution Reaction.

The rational design of multi-site electrocatalysts with three different functions for facile H2O dissociation, H-H coupling, and rapid H2 release is desirable but difficult to achieve. This strategy can accelerate the sluggish kinetics of the hydrogen evolution reaction (HER) under alkaline conditions. To resolve this issue, a Mo/Ru-based catalyst with three different active sites (Ru/Mo2C/MoO2) is rationally designed and its performance in alkaline HER is evaluated. The experimental results and density functional theory calculations revealed that, at the heterogeneous Mo2C/MoO2 interface, the higher valence state of Mo (MoO2) and the lower valence state of Mo (Mo2C) exhibited strong OH- and H-binding energies, respectively, which accelerated H2O dissociation. Moreover, the interfacial Ru possessed an appropriate hydrogen binding energy for H-H coupling and subsequent H2 evolution. Thus, this catalyst significantly accelerated the Volmer step and the Tafel step and, consequently, HER kinetics. This catalyst also demonstrated low overpotentials of 19 and 160mV at current densities of 10 and 1000mA cm-2, respectively, in alkaline media and long-term stability superior to that of most state-of-the-art alkaline HER electrocatalysts. This work provides a rational design principle for advanced multi-site catalytic systems, which can realize multi-electron electrocatalytic reactions.

Multi-interface and rich-defects 1T phase MoS2 combine with FeS anchored on reduced graphene oxide for efficient alkaline hydrogen evolution

Exploring and fabricating noble-metal-free and cost-effective electrocatalysts to minimise the excessive potential required is of great significance for alkaline hydrogen evolution reaction (HER). Herein, we report FeS/1T-MP MoS2@rGO heterostructure with 1T and 2H mixed phase MoS2 (1T-MP MoS2) combining with FeS anchored on reduced graphene oxide (rGO) matrix, which is synthetized by utilizing Anderson polyoxometalate as Fe–Mo precursor by a facile hydrothermal method. The FeS/1T-MP MoS2@rGO heterostructure in the form of interconnected nanosheet arrays with multiple interfaces and rich-defects, which is in favor of the immersion of the electrolyte and exposing more active sites. Benefiting from the synergistic advantages of 1T-MoS2, FeS and rGO, FeS/1T-MP MoS2@rGO heterostructure delivers enhanced conductivity, enlarged electrochemical active surface area, and eventually promote the HER kinetics. As expected, FeS/1T-MP MoS2@rGO heterostructure emerges prominent HER activity with low overpotentials of 102 and 256 mV to achieve current density of 10 and 100 mA cm−2, outperforming vast majority of the advanced 1T MoS2-based alkaline HER electrocatalysts.

Unlocking Efficient Alkaline Hydrogen Evolution Through Ru-Sn Dual Metal Sites and a Novel Hydroxyl Spillover Effect.

Alkaline hydrogen evolution reaction (HER) has great potential in practical hydrogen production but is still limited by the lack of active and stable electrocatalysts. Herein, the efficient water dissociation process, fast transfer of adsorbed hydroxyl and optimized hydrogen adsorption are first achieved on a cooperative electrocatalyst, named as Ru-Sn/SnO2 NS, in which the Ru-Sn dual metal sites and SnO2 heterojunction are constructed based on porous Ru nanosheet. The density functional theory (DFT) calculations and in situ infrared spectra suggest that Ru-Sn dual sites can optimize the water dissociation process and hydrogen adsorption, while the existence of SnO2 can induce the unique hydroxyl spillover effect, accelerating the hydroxyl transfer process and avoiding the poison of active sites. As results, Ru-Sn/SnO2 NS display remarkable alkaline HER performance with an extremely low overpotential (12mV at 10mA cm-2) and robust stability (650h), much superior to those of Ru NS (27mV at 10mA cm-2 with 90h stability) and Ru-Sn NS (16mV at 10mA cm-2 with 120h stability). The work sheds new light on designing of efficient alkaline HER electrocatalyst.

Navigating Alkaline Hydrogen Evolution Reaction Descriptors for Electrocatalyst Design

The quest for efficient green hydrogen production through Alkaline Water Electrolysis (AWE) is a critical aspect of the clean energy transition. The hydrogen evolution reaction (HER) in alkaline media is central to this process, with the performance of electrocatalysts being a determining factor for overall efficiency. Theoretical studies using energy-based descriptors are essential for designing high-performance alkaline HER electrocatalysts. This review summarizes various descriptors, including water adsorption energy, water dissociation barrier, and Gibbs free energy changes of hydrogen and hydroxyl adsorption. Examples of how to apply these descriptors to identify the active site of materials and better design high-performance alkaline HER electrocatalysts are provided, highlighting the previously underappreciated role of hydroxyl adsorption-free energy changes. As research progresses, integrating these descriptors with experimental data will be paramount in advancing AWE technology for sustainable hydrogen production.

A Molecular Engineered Strategy to Remolding Architecture of RuP2 Nanoclusters for Sustainable Hydrogen Evolution

AbstractTransition metal phosphides (TMPs) are promising hydrogen evolution reaction (HER) electrocatalysts, but the unsatisfying activity and durability at industrial‐scale current densities hinder their application. Downsizing TMPs to nanoclusters can substantially enhance their activity; yet, the high surface free energy tends to initiate agglomeration thereby limiting their service life. Herein, a molecular engineering strategy to synthesize robust sulfur‐doped RuP2 (S‐RuP2) nanoclusters, which can continuously provide ampere‐level current densities of 1.0, 2.0, and 3.0 A cm−2 for at least 480 h with low overpotentials of 55.6 ± 1.0, 90.6 ± 1.2, and 122.8 ± 1.0 mV, respectively, is proposed. In particular, it exhibits a remarkable charge transfer amount (representing a long service life), outperforming all reported alkaline HER electrocatalysts. Remoulding the RuP2 architecture by sulfur atom can significantly lift the d‐band center of Ru and the p‐band center of P, therefore strengthening the adsorption of H2O, H, and OH to reduce the barriers of water dissociation and H migration. The authors‘ research unveils the enormous potential of molecule‐based porous materials for designing high‐performance nano‐structured catalysts.

Morphological and Surface Electronic Structure Design of Alloys Electrocatalyst for Alkaline HER

Among the various hydrogen production methods, water electrolysis provides numerous advantages, including high purity of the produced hydrogen and low carbon emission. In this context, one of the concerns is associated with the replacement, or partial replacement, of noble-metal electrocatalyst for hydrogen evolution reaction (HER) by low-cost, commercially viable ones. To achieve this objective, alloying provides a direct way to tailor the electronic structure of active site and hence is expected to effectively reduce the usage of noble metal. Furthermore, increasing the surface area through morphology design is considered a promising method for enhancing catalyst activity. Among the diverse strategies to increase the surface area, dealloying plays a unique role by generating porous structure, thereby offering advantages in terms of cost-effectiveness and controllable structure. In this study, we have synthesized various Zn-Ni based alloy electrocatalysts using a facile solvothermal method, followed by a dealloying process. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry are used to examine the morphology, composition, and electronic structure. The electrochemical performance is investigated using linear sweep voltammetry, electrochemical impedance spectroscopy, cyclic voltammetry, and electrochemical specific surface area analyses. We demonstrate that resulting HER alloy electrocatalyst exhibits a low overpotential and Tafel slope, and good stability over 200 hours.

Tuning the Local Environment of Pt Species at CNT@MO2-x (M = Sn and Ce) Heterointerfaces for Boosted Alkaline Hydrogen Evolution.

As the most promising hydrogen evolution reaction (HER) electrocatalysts, platinum (Pt)-based catalysts still struggle with sluggish kinetics and expensive costs in alkaline media. Herein, we accelerate the alkaline hydrogen evolution kinetics by optimizing the local environment of Pt species and metal oxide heterointerfaces. The well-dispersed PtRu bimetallic clusters with adjacent MO2-x (M = Sn and Ce) on carbon nanotubes (PtRu/CNT@MO2-x) are demonstrated to be a potential electrocatalyst for alkaline HER, exhibiting an overpotential of only 75 mV at 100 mA cm-2 in 1 M KOH. The excellent mass activity of 12.3 mA μg-1Pt+Ru and specific activity of 32.0 mA cm-2ECSA at an overpotential of 70 mV are 56 and 64 times higher than those of commercial Pt/C. Experimental and theoretical investigations reveal that the heterointerfaces between Pt clusters and MO2-x can simultaneously promote H2O adsorption and activation, while the modification with Ru further optimizes H adsorption and H2O dissociation energy barriers. Then, the matching kinetics between the accelerated elementary steps achieved superb hydrogen generation in alkaline media. This work provides new insight into catalytic local environment design to simultaneously optimize the elementary steps for obtaining ideal alkaline HER performance.

Ru-induced lattice expansion of metallic Co with favorable surface property for high-efficiency water electrolysis

The development of high-performance electrocatalysts for alkaline hydrogen evolution reaction (HER) is an important step towards achieving hydrogen economy but remains major challenge. This study reports the growth of ultralow Ru (1 wt%) modified Co nanostructures (Rud-Co) with coral-like nanoarray structures on carbon cloth via lattice expansion tactics. Specifically, the as-fabricated Rud-Co electrode exhibits extraordinary electrocatalytic activity, with an overpotential of 25 mV at a current density of 10 mA cm−2 and a small Tafel slope of 31 mV dec−1 in alkaline media, which is superior to the benchmark Pt/C. Density functional theory (DFT) calculations disclose that Ru can shift the d-band center of Co to higher fermi level, which promotes electron transfer, H2O dissociation and *H adsorption during catalysis. This work provides a promising strategy for the development of efficient transition metal-based alkaline HER electrocatalysts via accelerating electron transfer and promoting mass transportation.

Unveiling the effect of solvent for hydrogen evolution in Pt-doped MXenes and corresponding high-entropy phase

Effect of solvent at the water/solid interface plays a non-negligible role in chemical reactions. Explicit solvation has been proved for its important effect on thermodynamics and kinetics of catalytic reactions. However, systematic studies about this perspective are still absence. In this work, using the model of single platinum atom immobilized on the metal vacancies of a series of MXenes, we systematically investigate the implicit/explicit solvent effect on their catalytic performance of the hydrogen evolution reaction (HER). We find that the solvent effect plays a significant role in affecting the calculation results for some systems. For TiNbC–PtNb, the value of ΔGH* decreases from −0.121 to −0.511 (−0.583) eV when considering implicit (explicit) correction, implying the decisive role of solvent effect for calculating HER in this system. Bader charge analysis and AIMD simulations reveal that TiNbC–PtNb surface is sensitive to H2O, thus causing this abnormal case. Surprisingly high-entropy phases of MXene overall are less sensitive to solvent compared to the pure phases, which could be due to their alloyed lattice with a strong ability against electronic and lattice fluctuations induced by solvent. Several systems like V2C–PtV, TiMoC–PtMo, and VNbC–PtV are predicted to be excellent electrocatalysts for alkaline HER with the appropriate Gibbs free energy of hydrogen adsorption and kinetic barrier of water dissociation. The perspective exemplified in this work highlights that more feasible operando should be considered, e.g., influence of water, to better simulate the reaction process. Our work suggests that Pt-doped MXenes are perfect systems for hosting atomic catalyst as well.

Defect engineering of 1T′ MX 2 (M = Mo, W and X = S, Se) transition metal dichalcogenide-based electrocatalyst for alkaline hydrogen evolution reaction

The alkaline electrolyzer (AEL) is a promising device for green hydrogen production. However, their energy conversion efficiency is currently limited by the low performance of the electrocatalysts for the hydrogen evolution reaction (HER). As such, the electrocatalyst design for the high-performance HER becomes essential for the advancement of AELs. In this work, we used both hydrogen (H) and hydroxyl (OH) adsorption Gibbs free energy changes as the descriptors to investigate the catalytic HER performance of 1T′ transition metal dichalcogenides (TMDs) in an alkaline solution. Our results reveal that the pristine sulfides showed better alkaline HER performance than their selenide counterparts. However, the activities of all pristine 1T′ TMDs are too low to dissociate water. To improve the performance of these materials, defect engineering techniques were used to design TMD-based electrocatalysts for effective HER activity. Our density functional theory results demonstrate that introducing single S/Se vacancy defects can improve the reactivities of TMD materials. Yet, the desorption of OH becomes the rate-determining step. Doping defective MoS2 with late 3d transition metal (TM) atoms, especially Cu, Ni, and Co, can regulate the reactivity of active sites for optimal OH desorption. As a result, the TM-doped defective 1T′ MoS2 can significantly enhance the alkaline HER performance. These findings highlight the potential of defect engineering technologies for the design of TMD-based alkaline HER electrocatalysts.

A highly active and durable NiMoCuCo catalyst with moderated hydroxide adsorption energy for efficient hydrogen evolution reaction

A charge valence state and surface-electronegativity-modulated NiMoCuCo composite is proposed as an active and durable alkaline hydrogen evolution reaction electrocatalyst with moderated hydroxide adsorption energy.

An advanced Ru-based alkaline HER electrocatalyst benefiting from Volmer-step promoting 5d and 3d co-catalysts.

In this study, a trimetallic catalyst, NiWRu@NF, is electrodeposited onto nickel foam using chronoamperometry to enhance the hydrogen evolution reaction (HER) in alkaline water electrolysis. The catalyst combines nickel, tungsten, and ruthenium components, strategically designed for efficiency and cost-effectiveness, hydroxyl transfer and water dissociation, and acceleration of hydrogen combination, respectively. Evaluation of NiWRu@NF reveals exceptional performance, with a low overpotential of -50 mV and high current density of -10 mA cm-2, signifying its efficiency in promoting HER. Tafel values further corroborate the catalyst's effectiveness, indicating a rapid reaction rate of hydrogen evolution in such a highly alkaline medium compared to other controls studied along with it. This study underscores the significance of NiWRu@NF in advancing alkaline HER kinetics, paving the way for more efficient electrolysis processes.

Tailoring Binding Abilities By Incorporating Oxophilic Transition Metals on 3D Nanostructured Ni Arrays for Accelerated Alkaline Hydrogen Evolution Reaction

Developing efficient and inexpensive electrocatalysts for the hydrogen evolution reaction (HER) in alkaline water electrolysis plays a key role for renewable hydrogen energy technology. The slow reaction kinetics of HER in alkaline solutions, however, has hampered advances in high-performance hydrogen production. Herein, we investigated the trends in HER activity with respect to the binding energies of Ni-based thin film catalysts by incorporating a series of oxophilic transition metal atoms. It was found that the doping of oxophilic atoms enables the modulation of binding abilities of hydrogen and hydroxyl ions on the Ni surfaces, leading to the first establishment of a volcano relation between OH-binding energies and alkaline HER activities. In particular, Cr-incorporated Ni catalyst shows optimized OH-binding as well as H-binding energies for facilitating water dissociation and improving HER activity in alkaline media. Further enhancement of catalytic performance was achieved by introducing an array of three-dimensional (3D) Ni nanohelixes (NHs) that provide abundant surface active sites and effective channels for charge transfer and mass transport. The Cr dopants incorporated into the Ni NHs accelerate the dissociative adsorption process of water, resulting in remarkably enhanced catalytic activities in alkaline medium. Our approach can provide a rational design strategy and experimental methodology toward efficient bimetallic electrocatalysts for alkaline HER using earth-abundant elements.Reference Journal of the American Chemical Society 3, 1399-1408 (2021) [Front Cover]

Optimizing Pt-Based Alloy Electrocatalysts for Improved Hydrogen Evolution Performance in Alkaline Electrolytes: A Comprehensive Review.

The splitting of water through electrocatalysis offers a sustainable method for the production of hydrogen. In alkaline electrolytes, the lack of protons forces water dissociation to occur before the hydrogen evolution reaction (HER). While pure Pt is the gold standard electrocatalyst in acidic electrolytes, since the 5d orbital in Pt is nearly fully occupied, when it overlaps with the molecular orbital of water, it generates a Pauli repulsion. As a result, the formation of a Pt-H* bond in an alkaline environment is difficult, which slows the HER and negates the benefits of using a pure Pt catalyst. To overcome this limitation, Pt can be alloyed with transition metals, such as Fe, Co, and Ni. This approach has the potential not only to enhance the performance but also to increase the Pt dispersion and decrease its usage, thus overall improving the catalyst's cost-effectiveness. The excellent water adsorption and dissociation ability of transition metals contributes to the generation of a proton-rich local environment near the Pt-based alloy that promotes HER. Significant progress has been achieved in comprehending the alkaline HER mechanism through the manipulation of the structure and composition of electrocatalysts based on the Pt alloy. The objective of this review is to analyze and condense the latest developments in the production of Pt-based alloy electrocatalysts for alkaline HER. It focuses on the modified performance of Pt-based alloys and clarifies the design principles and catalytic mechanism of the catalysts from both an experimental and theoretical perspective. This review also highlights some of the difficulties encountered during the HER and the opportunities for increasing the HER performance. Finally, guidance for the development of more efficient Pt-based alloy electrocatalysts is provided.

Synergistic dual-regulating the electronic structure of NiMo selenides composite for highly efficient hydrogen evolution reaction

Large-scale hydrogen production via electrochemical water splitting is important to renewable energy generation and the global drive toward low carbon emission. However, because of the sluggish kinetics and high energy consumption, efficient and economical electrocatalysts are required for the hydrogen evolution reaction (HER) in order to make it commercially viable. Herein, we present a dual-regulation strategy to optimize the electronic structure of NiMo selenides (NMS) composite for HER. By capitalizing on the electronic interactions between Ni and Mo atoms through the in situ phase separation of Ni0.85Se and MoSe2 from NiMoO4, the electronic configuration is optimized. The selective reduction is simultaneously performed to tune the oxidation states of Ni and Mo, which is more favorable for the adsorption of water molecules and desorption of hydrogen. The NMS electrocatalyst shows an overpotential of 124 mV for a current density of 10 mA cm−2, a small Tafel slope of 63 mV dec−1 in alkaline electrolytes, Faradaic efficiency of 98.9 % in hydrogen production, as well as excellent long-term stability for 170 h. The results reveal a valuable strategy of synergistic dual-regulating the electronic structure of the active sites to design and prepare inexpensive and high-performance electrocatalysts for alkaline HER and related applications.

Hydrogen spillover in MoOxRh hierarchical nanosheets boosts alkaline HER catalytic activity

The low intrinsic catalytic performance and stability are the two dominant obstacles for alkaline hydrogen evolution reaction (HER) electrocatalyst. Herein, amorphous molybdenum oxide (MoOx) has been introduced to rhodium hierarchical nanosheets (MoOxRh-HNS) at atomic level efficiently reducing the barrier for hydrogen spillover from Rh to MoOx; thereby, MoOxRh-HNS exhibit superior HER activity with mass activity of 23.9 A mgnoble metal−1 at overpotential of 200 mV, which is boosted by 10.8- and 14.9-fold with relative to Rh-HNS and Pt/C in alkaline media, respectively. Meanwhile, Tafel slope is as low as 22.5 mV dec−1 for MoOxRh-HNS revealing a hydrogen-spillover-involving HER mechanism proved by the electrochemical test as well as operando electrochemical impedance spectroscopy. Density functional theory calculation indicates the adsorbed hydrogen on MoOxRh promotes the water dissociation and balances the hydrogen binding strength to a moderate level. Simultaneously, the hierarchical nanosheet structure contributes a robust HER stability at 500 mA cm−2. This work offers a new methodology to construct a high-performance alkaline HER electrocatalyst with industrial-level current density.