HER Catalysts Research Articles

Trace oxophilic metal induced surface reconstruction at buried RuRh cluster interfaces possesses extremely fast hydrogen redox kinetics

Developing high-efficiency electrocatalysts is the key to generating and consuming hydrogen by accelerating the reaction kinetics of the hydrogen oxidation and evolution reactions (HOR/HER). Although the kinetics process of the adsorbed intermediates (Had)-water-oxophilic metal has been investigated in the alkaline media, the hydroxyl species (Had or OH- or OHad)-activity relationship for oxophilic metal alloy electrocatalysis during multiple HOR and HER processes is still unclear. In this regard, our density functional theory (DFT) calculation results show that, due to partial substitution of Ru (Rh) clusters at buried interfaces by oxophilic-metal (OM) species, the long-range order of Ru (Rh) clusters surface atoms can be broken, and then the active atom reconstruction at buried interfaces is triggered, which decreases the oxidation intermediates of Ru (Rh) and gives rise to the increased activity for alkaline HER/HOR. At the same time, an OH--adsorption promoter forms, also favorable for OER. Encouraged by the first-principles calculation results, an ultralow-loaded OM species (0.13 wt% Co, 0.23 wt% Mn, 2.4 wt% Cr or 1.3 wt% Fe) incorporated RuRh cluster (RuRh-OM) catalyst is built by a mixed-solvent strategy. Impressively, after incorporating OM (Co; Mn; Cr and Fe), these catalysts exhibit higher HOR activity than pristine RuRh and commercial Pt even at higher potentials in 0.1 M KOH solutions, which outperforms most reported HOR catalysts and ~ 2 times higher than that of commercial Pt. Meanwhile, RuRh-Co also exhibits the highest HER activity among all reported Ru-based HER catalysts, and greatly improved OER and overall water spitting performances in alkaline solutions (1 M KOH for HER and overall water spitting, 0.1 M KOH for OER), exceeding RuRh and commercial noble metal catalysts.

Synergistic effect in ultrafine PtNiP nanowires for highly efficient electrochemical hydrogen evolution in alkaline electrolyte

Platinum-based catalysts play an important role in electrochemical hydrogen evolution reaction, which is a renewable and clean way to produce H2. Herein, we have successfully synthesized the ultrafine PtNiP NWs with diameter less than 5 nm via a simple two-step hydrothermal reaction method. Impressively, the PtNiP NWs exhibit one of the best electrocatalytic activity toward HER under alkaline conditions, which can reach current density of 500 mA cm−2 only at the −0.153 V vs RHE with Tafel slop of only 30 mV dec−1. The DFT calculation results show synergistic effect of Pt, Ni and P atoms, where Ni atoms are conducive to the adsorption of H2O and P atoms are helpful for the dissociation of H2O, significantly improving kinetic processes of hydrogen evolution reaction. This work could be instructive and meaningful to design highly efficient and stable HER catalyst in alkaline condition for practical applications.

An overview of the active sites in transition metal electrocatalysts and their practical activity for hydrogen evolution reaction

Locating the active sites and understanding the reaction mechanism are crucial for the design and preparation of higher hydrogen evolution activity catalysts. If these theoretical knowledges can be combined with practical large-scale hydrogen production, the development of electrochemical water splitting will be further promoted. In this review, we have first summarized the active sites of recent reported HER catalysts, including transition metals molybdenum, iron, nickel, cobalt and noble metal-based materials. At the same time, the mechanisms of hydrogen evolution followed by each catalyst and corresponding strategies for improving their catalytic activity are also discussed. In addition, from the point of practical application, the testing conditions, achievements already made and challenges that to be faced for each type of material are also proposed. The implementation of this work is helpful for researchers to master the electrocatalyst from a deeper perspective (including hydrogen adsorption energy, water adsorption energy, water dissociation energy, active surface and active site.), thus promoting the development of water electrolysis.

Natural DNA-derived highly-graphitic N, P, S-tridoped carbon nanosheets for multiple electrocatalytic applications

In the electrocatalytic oxygen reduction and hydrogen evolution reactions (ORR/HER), metal-free carbon-based materials presented great potentials as alternatives to Pt because of their flexible adjustability of electronic and geometric properties. The pursuit of high-performance carbons demand for high-level doping, large surface area and high graphitization, but the improvement of the former two aspects would inevitably impair the third one, which seems a contradictive proposition. Herein, by a facile “mix-and-pyrolyze” method, natural DNA was first developed to synthesize N, P, S-tridoped carbons (NPSC) with porous sheet structures, high graphitization, large surface areas and abundant high-quality dopants simultaneously. Thus, the newly-prepared NPSC displays superior alkaline ORR performance comparable to Pt/C together with excellent acidic activity and better stability. Meanwhile, NPSC is one of most active acidic HER catalysts and the best alkaline HER catalyst among carbon counterparts. Density function theory computation reveled the origins of superior performance are attributed to positively charged C sites neighboring to S for ORR and P sites for HER because of DNA-derived advantaged structural features. The as-fabricated rechargeable zinc–air battery based on current tridoped carbon has closed peak power density and specific capacity but much better charge–discharge stability compared with Pt/C.

Dual-metallic single Ru and Ni atoms decoration of MoS2 for high-efficiency hydrogen production

The limitation of single-atom catalysts hinders its promotion and application in the HER field. Herein, we fabricated a dimetallic single-atom catalyst where monoatomic Ru and Ni co-modify MoS2 using a mild method (Ru/Ni-MoS2). Experiments combined with theoretical calculations indicated that the single Ru atoms were anchored through single Ni atoms with strong electronegativity, and most of the Ru atoms coordinated with the S were distributed on the Ni atop sites. And the synergistic effect of the Ru/Ni-MoS2 with S atoms bonded with Ni as hydrogen acceptor and single-atoms Ru as hydroxyl acceptor, effectively reduced the intermediate energy barrier of the water dissociation step. The as-fabricated Ru/Ni-MoS2 exhibited a super-low overpotential of 32 mV at 10 mA cm−2 with the corresponding Tafel slope of 41 mV·dec-1 as well as negligible current attenuation over 20 h, far surpassing that of Ru-MoS2 and Ni-MoS2. This work not only provides a high-efficiency HER catalysts, but also a new idea based on electronegativity difference and bimetallic single-atom regulation to design catalyst.

Enabling Efficient Water Splitting with Advanced Materials Designed for High pH Membrane Interface

This research focuses on durable, high-performance materials and interfaces for advanced water splitting, enabling a clear pathway for achieving <$2/KgH2 (on scale) via anion exchange membrane (AEM)-based electrolysis. We aim to advance this goal via an improved fundamental understanding of both hydrogen and oxygen evolution reactions (HER/OER) leading to platinum group metal (PGM)-free catalyst materials. Here, we use NiFeCo and NiMo as OER and HER catalysts, respectively, in a full alkaline electrolysis cell. A thermally stable, multi-cation AEM is used to operate the cell at elevated temperatures thereby lowering the operating potential by increasing the kinetics of the respective catalytic reactions. The transition metal catalysts, paired with this novel AEM, have been used to achieve an operating potential of 1.79 V at 1 A/cm2. This potential is 300 mV lower than similar electrolysis cells equipped with PGM-based catalysts. We have also demonstrated the efficacy of the less caustic potassium carbonate solution as a replacement for potassium hydroxide as an electrolyte. By using a carbonate-based electrolyte, the hydroxide ion required for the anodic reaction is continuously replenished by re-establishing an equilibrium with water. This consideration, coupled with the reduced alkalinity of the carbonate solution, yields an electrolysis cell capable of sustained operation with minimal increase in operating potential.

Earth-abundant nickel cobalt disulfide nanoporous networks catalyst for efficient hydrogen evolution

Using transition metal disulfide (TMD) as a substitute for noble-metal-based catalysts is considered a promising strategy for achieving practical hydrogen production from water splitting. Herein, an earth-abundant, highly crystalline, bimetal disulfide nanoporous networks (Ni0.33Co0.67S2) was constructed via dealloying and low-temperature chemical vapor deposition (CVD) methods. As expected, the as-prepared Ni0.33Co0.67S2 can be served as an efficient, and robust electrocatalyst for HER, and exhibiting a lower overpotential (191.2 mV at 10 mA cm−2) and Tafel slope (93.64 mV dec-1) than that of NiS2 and CoS2 synthesized through the similar methods. Moreover, the potential increase is only 50 mV in 12 h of long-term durability test for Ni0.33Co0.67S2 catalyst. Further analysis shows the significantly improved performance of Ni0.33Co0.67S2 should be attributed to the enhanced charge transfer, as well as increased electrochemical active specific surface area. Therefore, the combination of versatile dealloying inheritance effect and CVD modification strategy could provide a promising channel for preparing practical HER catalyst.

Enhancement in the catalytic activity of two-dimensional α-CN by B, Si and P doping for hydrogen evolution and oxygen evolution reactions

Employing the Density Functional Theory investigations, we have designed 2D α-CN with the dopants P, Si and B as catalyst for HER and OER activities. Doping of P and B over α-CN modifies its electronic properties and reduces band gap (3.78 eV) of α-CN to the required band gap for HER and OER activities. The modification of electronic properties is discussed by the analysis of partial density of states, Löwdin charge and charge density plot. To understand HER and OER activities better, we computed Gibbs free energy change after adsorption of H/O in various doped α-CN systems. We observe that the P doping at C site and B doping at N site of α-CN are best suited for HER and OER respectively. The HER (OER) activity increases by 88.33% (29.35%) for P doped at C site (B doped at N site) of α-CN in comparison to pristine α-CN.

Atomically Dispersed Platinum Modulated by Sulfide as an Efficient Electrocatalyst for Hydrogen Evolution Reaction.

Catalytically active metals atomically dispersed on supports presents the ultimate atom utilization efficiency and cost‐effective pathway for electrocatalyst design. Optimizing the coordination nature of metal atoms represents the advanced strategy for enhancing the catalytic activity and the selectivity of single‐atom catalysts (SACs). Here, we designed a transition‐metal based sulfide‐Ni3S2 with abundant exposed Ni vacancies created by the interaction between chloride ions and the functional groups on the surface of Ni3S2 for the anchoring of atomically dispersed Pt (PtSA‐Ni3S2). The theoretical calculation reveals that unique Pt‐Ni3S2 support interaction increases the d orbital electron occupation at the Fermi level and leads to a shift‐down of the d ‐band center, which energetically enhances H2O adsorption and provides the optimum H binding sites. Introducing Pt into Ni position in Ni3S2 system can efficiently enhance electronic field distribution and construct a metallic‐state feature on the Pt sites by the orbital hybridization between S‐3p and Pt‐5d for improved reaction kinetics. Finally, the fabricated PtSA‐Ni3S2 SAC is supported by Ag nanowires network to construct a seamless conductive three‐dimensional (3D) nanostructure (PtSA‐Ni3S2@Ag NWs), and the developed catalyst shows an extremely great mass activity of 7.6 A mg−1 with 27‐time higher than the commercial Pt/C HER catalyst.

Nanoscale CuTe electrocatalyst immobilized at conductor surface for remarkable hydrogen evolution reaction

Hydrogen generation from electrocatalytic water splitting is of supreme significance for resolving energy crisis and environmental concerns. However, developing earth-abundant, efficient, and durable electrocatalyst for high-performance hydrogen evolution and complete water splitting catalysis is a rare instance. We present here the first demonstration of unique copper tellurides nano-structures (CuTe-NS) based electrocatalyst executing HER with high activity and remarkable stability. CuTe-NS based electrocatalysts grown over conductive NiF via drop-casting approach and employed for HER, while achieving a current decade and a current density of 100 mA/cm2 just at 0.25 V vs. RHE and 0.27 V vs. RHE, which is comparable to the benchmark Pt/C based HER catalyst. The catalyst demonstrates well-balanced kinetic behavior, low Tafel slope of 36 mV/dec, low charge transfer resistance of 1.71 Ω, high roughness factor, and remarkable stability for more than 60 h of electrolysis. Furthermore, post-catalysis characterizations demonstrate no change in catalyst integrity, morphological, and structural attributes even after many hours of electrolysis which show sustainable behavior of catalyst for long term HER activity. Because of electrochemical and structural stabilities after long term electrolysis experiments, accessible method of preparations, and cost-effectiveness, the catalysis is highly encouraging for real-life applications.

N-doped carbon-encapsulated nickel on reduced graphene oxide materials for efficient CO2 electroreduction to syngas with potential-independent H2/CO ratios

Electrochemical CO2 reduction (ECR) is a sustainable method for obtaining syngas, which is largely desired for producing high energy-dense hydrocarbons and alcohols through the industrialized process. However, it is still a challenge to adjust the H2/CO ratio in a wide range while holding a large current density. Guiding by the density functional theory (DFT) calculations, the electrocatalyst of N-doped carbon-encapsulated metallic Ni particles supported on reduced graphene oxide (Ni@N–C/rGO) is developed for ECR to tunable syngas. The quantitative Ni@N–C responses to the controllable catalytic activity of ECR to CO, while the rGO serves as both HER catalyst and support of Ni@N-C. The Ni@N-C/rGO material exhibits high CO2 reduction activity and stability, thereby achieving a specific current of 23 mA cm−2 and CO Faradaic efficiency (FE(CO)%) of 90% at − 0.97 V vs. RHE. More importantly, the H2/CO ratio of the syngas can be adjusted in a large range of 9/1–1/9 without potential-dependence while maintaining large current densities (> 15 mA cm−2).

Mixed MoS₂/MoO₃ Nanostructures for Hydrogen Evolution Reaction.

The electrolysis of water has paved the way towards a clean, efficient and renewable energy source for the future technologies. Therefore, an efficient electrocatalyst is needed. MoS₂ based nonprecious materials are earth-abundant, low cost and promising for the hydrogen evolution reaction. In this study, the effect of sulfur source on the catalytic properties of the MoS₂ nanostructures is investigated. Two different sulfur precursors (i.e., thiourea and L-cysteine) were used for the synthesis of MoS₂ nanostructures. The optimization of the sulfur precursor content was carried out to report the best for the development of the future generation of HER catalysts. The cysteine assisted synthesis results the mixed MoO₃/MoS₂ composite structure which has shown significant effect on the catalytic activity. The low concentrations of cysteine and thiourea have shown excellent catalytic activity and stability in 0.5 M H₂SO₄. TheMoS₂ nanostructures with the cysteine as sulfur precursor have shown low Tafel slope of 81 mV dec-1 and a current density of 30 mA cm-2 is obtained at 0.45 V versus RHE. The superior performance of cysteine-based MoS₂ sample is due to the rapid charge transfer as confirmed by EIS and excellent conductivity as witnessed by low optical band gap. These findings strengthen the understanding of fundamental science of Mo-based catalysts for the development of the future generation of electrocatalysts and energy conversion technologies.

Plasma-induced moieties impart super-efficient activity to hydrogen evolution electrocatalysts

Abstract Having a high combustion value (1.4 × 108 J/kg) with an intrinsically green nature, hydrogen has been widely regarded as the next generation energy alternative to the conventional fossil fuels that have caused severe environmental issues associated with the rapidly increasing CO2 emissions, including global warming, sea level rising and species extinction. Thus, it is important to develop highly efficient and cost-effective catalysts for hydrogen generation. Herein, we fabricated a novel NiMoO4 catalyst on Ni foams, followed by NH3–plasma treatment to introduce NH2 functional groups, which were then transformed into –NH3 moieties during the HER process to afford a superb HER activity in alkaline solution, approaching the theoretical limit. The resultant NHx-NiMoO4 HER catalyst was demonstrated to be super-active with a record high HER performance (η @ 10 mA cm−2 = 18 mV, Tafel slope = 28.3 mV/decade) and promising for sea-water splitting. The theoretical studies suggest that NH3 moieties suffered from reorganization towards minimizing the energy barriers for both Volmer and Tafel/Heyrovsky steps. The plasma method may be extended to the design of novel catalysts for many other important chemical or electrochemical reactions.

Self-supported Mo0.2Co0.8P nanowire arrays on carbon cloth as a high-performance and durable hydrogen evolution reaction electrocatalyst in wide-range pH

We successfully prepared a Mo 0.2 Co 0.8 P nanowires growing vertically on carbon cloth through hydrothermal and phosphorization processes. This work provides a feasible way for the preparation of non-precious metal electrocatalysts. • Mo 0.2 Co 0.8 P/CC nanowire arrays was prepared via hydrothermal and low-temperature phosphorization methods. • Mo 0.2 Co 0.8 P/CC possesses outstanding HER activity and strong stability in both 0.5 M H 2 SO 4 and 1 M KOH. • The introduction of Mo atoms lead defects and distortions on the material surface. • The strong synergistic effect between Co and Mo atoms. Exploring an efficient non-noble metal catalyst for hydrogen production by electrolysis of water is one of the effective ways to solve energy shortage and environmental problems. Herein, we report a Mo 0.2 Co 0.8 P nanowires based on carbon cloth (Mo 0.2 Co 0.8 P NWAs/CC) as an efficient HER catalyst in wide-range pH, via facile hydrothermal and phosphorization methods. This Mo 0.2 Co 0.8 P NWAs/CC exhibits the outstanding electrocatalytic performance with low overpotentials of 60 and 66 mV at 10 mA cm −2 and small Tafel slopes of 69.5 and 78.3 mV dec −1 in acidic and alkaline solution, respectively. Moreover, the long-term stability of Mo 0.2 Co 0.8 P NWAs/CC also presents excellent for 50 h at η 10 . The superior electrochemical properties of Mo 0.2 Co 0.8 P NWAs/CC material are attributed to its smaller nanoscale, lattice defects and distortions, and strong synergistic effect between Co and Mo atoms. This work provides an effective electrocatalyst for the water electrolysis process.

In Situ Cation Intercalation in the Interlayer of Tungsten Sulfide with Overlaying Layered Double Hydroxide in a 2D Heterostructure for Facile Electrochemical Redox Activity.

The role of electrochemical interfaces in energy conversion and storage is unprecedented and more so the interlayers of two-dimensional (2D) heterostructures, where the physicochemical nature of these interlayers can be adjusted by cation intercalation. We demonstrate in situ intercalation of Ni2+ and Co2+ with similar ionic radii of ∼0.07 nm in the interlayer of 1T-WS2 while electrodepositing NiCo layered double hydroxide (NiCo-LDH) to create a 2D heterostructure. The extent of intercalation varies with the electrodeposition time. Electrodeposition for 90 s results in 22.4-nm-thick heterostructures, and charge transfer ensues from NiCo-LDH to 1T-WS2, which stabilizes the higher oxidation states of Ni and Co. Density functional theory calculations validate the intercalation principle where the intercalated Ni and Co d electrons contribute to the density of states at the Fermi level of 1T-WS2. Water electrolysis is taken as a representative redox process. The 90 s electrodeposited heterostructure needs the relatively lowest overpotentials of 134 ± 14 and 343 ± 4 mV for hydrogen and oxygen evolution reactions, respectively, to achieve a current density of ±10 mA/cm2 along with exceptional durability for 60 h in 1 M potassium hydroxide. The electrochemical parameters are found to correlate with enhanced mass diffusion through the cation and Cl--intercalated interlayer spacing of 1T-WS2 and the number of active sites. While 1T-WS2 is mostly celebrated as a HER catalyst in an acidic medium, with the help of intercalation chemistry, this work explores an unfound territory of this transition-metal dichalcogenide to catalyze both half-reactions of water electrolysis.

Charge redistribution of Ru nanoclusters on Co3O4 porous nanowire via the oxygen regulation for enhanced hydrogen evolution reaction

Ru-based catalysts are widely studied for hydrogen evolution reaction. However, there is still a lack of research on which chemical environment is more favorable for the catalytic performance of Ru. In this work, Ru nanoclusters are loaded on porous Co 3 O 4 nanowires (Ru/Co 3 O 4 NWs), spherical aberration-corrected transmission electron microscope and extended X-ray absorption fine structure confirm the coordination environment of Ru with oxygen bond. Compare to Co nanowires, Ru/Co 3 O 4 NWs have the better HER performance in alkaline medium (an overpotential of 30.96 mV at a current density of 10 mA cm −2 , electrochemical areas of 4.31 mF cm −2 ). Theoretical calculation also demonstrates the charge redistribution of Ru through the O binding, which has a smaller |ΔG H* | value. Besides, Ru clusters are loaded on Co foam and further oxygen doped to achieve efficient and stable HER activity. This work put a deep insight into the role of oxygen regulation of Ru-based HER catalysts. • Ru/Co 3 O 4 NWs were synthesized through cation replacement and controlling reduction. • The surrounding oxygen promoted the charge redistribution of Ru and enhanced its HER activity. • This oxygen-enhanced strategy provided a cost-effective prospect of industrial application.

Hydrogen evolution on Au/GC and PdAu/GC nanostructures in acid solution: AFM, XPS, and electrochemical study

HER was examined on various glassy carbon-supported Au and PdAu electrodes in acid solution. The Au/GC electrodes were obtained after Au was electrodeposited on a GC substrate by holding the potential for various times in 0.5 M H2SO4 solution containing AuCl4− ions. PdAu/GC electrodes were obtained after Pd has been added by a spontaneous deposition on previously prepared Au/GC electrodes. Surface morphology and chemical analysis of Au/GC and PdAu/GC electrodes were performed by atomic force microscopy and X-ray photoemission spectroscopy. Electrochemical characterization was performed by cyclic voltammetry in 0.5 M H2SO4 solution, while the linear sweep voltammetry was used to gain insight into the electrocatalytic activity of these electrodes for HER. 30minPd/10minAu/GC electrode consisting of 48% Pd and 65% Au, with the total coverage of the GC substrate with PdAu islands of 70%, showed the best catalytic activity for HER. A remarkable high activity and stability of this electrode makes it a promising catalyst for HER in acid solution.

Cobalt phosphide supported by two-dimensional molybdenum carbide (MXene) for the hydrogen evolution reaction, oxygen evolution reaction, and overall water splitting

CoP/Mo2CTx is prepared as efficient catalyst for HER, OER, and water splitting. DFT calculations revealed that it has optimal H* adsorption free energy and MXene plays a critical role to boost HER, while CoP is transformed into Co–OOH in OER.

Intercalation engineering of MXenes towards highly efficient photo(electrocatalytic) hydrogen evolution reactions

A brief description of the fabrication of intercalants of MXenes and their physical properties, along with their comprehensive applications, including their promising catalysts for HER with high efficiency.

Ru@N/S/TiO2/rGO: a high performance HER electrocatalyst prepared by dye-sensitization.

Hydrogen production from water-splitting is one of the most promising hydrogen production methods, and the preparation of the hydrogen evolution reaction (HER) catalyst is very important. Although Pt-based materials have the best catalytic activity for HER, their high price and scarcity greatly limit their large-scale industrial application prospects. Herein, a new method to prepare HER catalyst is described, where dyes used in dye-sensitized solar cells (DSSCs) were used as precursors. A high performance HER catalyst (Ru@N/S/TiO2/rGO, Ru nanoparticles (NPs) supported on N/S-doped TiO2/rGO hybrids) was prepared, and the stereoscopic molecular structure of the porphyrin dye, JR1, not only provides a prerequisite for the preparation of the hyperdispersed Ru NPs, but also successfully realizes N/S co-doping. The Ru@N/S/TiO2/rGO shows an excellent catalytic performance for the HER, which is almost the same as that with Pt/C. In 0.5 M H2SO4, the overpotential is 60 mV at 10 mA cm-2, and the Tafel slope is only 51 mV dec-1. In 1 M KOH, the overpotential is only 5 mV at 10 mA cm-2, and the Tafel slope is only 45 mV dec-1, and this performance is much better than most of the HER catalysts that have been reported. When Ru@N/S/TiO2/rGO is utilized as a catalyst in an alkaline water electrolyzer, a bias of only 1.52 V is able to complement overall water-splitting at 10 mA cm-2 (1.78 V, 100 mA cm-2). The molecular structure and coordination metal species of the dyes are easy to adjust, and the the stereoscopic structure is very helpful for inhibiting the aggregation of the metal NPs, and the strong anchoring effect with TiO2 or other carbon materials is also very helpful to achieve heteroatom doping. In addition, the process of dye-sensitization is simple and repeatable, and is a novel and efficient method to prepare the electrocatalyst.