Improvement In Hydrogen Evolution Reaction Activity Research Articles

Recent progress of molybdenum disulfide/carbon composites for electrochemical hydrogen evolution reaction

As a star two-dimensional material, molybdenum disulfide (MoS2) shows a good potential in the field of electrochemical hydrogen evolution reaction (HER) due to its low price, special physicochemical properties and a small theoretical Gibbs free energy of hydrogen adsorption. However, some disadvantages such as poor electroconductivity and inert basal planes hinder its further improvement of HER activity. Therefore, adopting carbon materials with good electrical conductivity and large specific surface area to composite with MoS2 is one of the popular strategies to improve the electrical conductivity and increase the exposure of catalytically active sites for constructing highly efficient MoS2-based electrocatalysts. Herein, in this review, we firstly gave a brief introduction of the MoS2 structure and the basic HER principle. Then, the synthesis method, catalytic performance and reaction mechanism of utilizing different carbon materials to improve the HER activity of MoS2 were summarized in detail. Finally, the existing problems and future opportunities for preparing highly active and low cost electrocatalysts assisted by carbon materials are prospected.

Space confined growth of RuO2/Ru carbon nanorods for highly efficient electrocatalytic hydrogen evolution

Exploring efficient and robust electrocatalysts with low cost for hydrogen evolution reaction (HER) is critical for practical application of electrochemical water splitting. Ru-based platinum group electrocatalysts shows great potential in HER, however, Ru suffer from sluggish kinetics of water dissociation for electrochemical reduction of water to hydrogen in alkaline environments. Here, oxygen atoms are introduced into Ru by simple secondary heat treatment to form Ru–O–C bonds to weak the strength of Ru–H bond. The overpotential of the catalyst is only 19 mV at 10 mA cm−2 and the stability is greatly improved. Theoretical calculations reveal that the Ru–O–C structure formed in RuO2 facilitates the dissociation of H–OH, which is the rate-determining step in alkaline electrolytes, leading to significant improvement in HER activity.

Enhancing hydrogen evolution reaction activity through defects and strain engineering in monolayer MoS2.

Molybdenum disulfide (MoS2) has recently emerged as a promising electrocatalyst for the hydrogen evolution reaction (HER). However, the poor in-plane electrical conductivity and inert basal plane activity pose major challenges in realizing its practical application. Herein, we demonstrate a new approach to induce biaxial strain into CVD-grown MoS2 monolayers by draping it over an array of patterned gold nanopillar arrays (AuNAs) as an efficient strategy to enhance its HER activity. We vary the magnitude of applied strain by changing the inter-pillar spacing, and its effect on the HER activity is investigated. To capitalize on the synergistic effect of improved ΔG H via strain engineering and leverage basal plane activation by introduction of sulphur vacancies, we further exposed the strained MoS2 monolayers to oxygen plasma treatment to create S-vacancies. The strained MoS2 on AuNAs with optimal inter-pillar spacing is exposed to oxygen plasma treatment for different durations, and we study its electrocatalytic activity towards the HER using on-chip microcell devices. The strained and vacancy-rich monolayer MoS2 draped on AuNAs with a 0.5 μm inter-pillar spacing and exposed to plasma for 50 s (S0.5μmV50-MoS2) is shown to exhibit remarkable improvement in HER activity, with an overpotential of 53 mV in 0.5 M H2SO4. Thus, the synergistic creation of additional vacancy defects, along with strain-induced active sites, results in enhancement in HER performance of CVD-grown monolayer MoS2. The present study provides a highly promising route for engineering 2D electrocatalysts towards efficient hydrogen evolution.

First principles study on high-efficient overall water splitting by anchoring cobalt boride with transition metal atoms

Developing efficient, low-cost electrocatalysts is of great significance for improving the efficiency of water electrolysis. In this work, the structure, electronic properties, hydrogen evolution reaction (HER), and oxygen evolution reaction (OER) activity of transition metal-doped cobalt boride (TM@CoB) were thoroughly investigated using density functional theory. Ni@CoB and Cu@CoB exhibited excellent catalytic activity for HER. Specifically, Ni@CoB demonstrated a ΔGH* value of 0.0537 eV, surpassing the most commonly used Pt catalyst. The reaction mechanism followed the Heyrovsky mechanism, and it also showed good OER activity, making it a potential candidate for OER electrocatalysts. Compared to the original CoB, Ni@CoB showed a 70 % improvement in HER activity and a 65 % improvement in OER activity. The Ni@CoB catalyst was synthesized, and its catalytic performance was experimentally validated. This work offers a new perspective and guidance for the development of bifunctional electrocatalysts.

Crystalline/amorphous CoP/MnOx heterostructure derived from phase separation for electrochemical catalysis of alkaline hydrogen evolution reaction

The electrochemical water splitting in alkaline media is troubled by the lack of efficient electrocatalysts for hydrogen evolution reaction (HER). Herein, a crystalline/amorphous CoP/MnOx heterostructure is converted from a single-phase bimetallic Co–Mn oxide by phase separation strategy. The CoP/MnOx heterostructure only requires an overpotential of 135 mV to reach 10 mA cm−2 in 1 M KOH, which is lower than that of CoP (184 mV). The interface effect between CoP and MnOx is beneficial to the improvement of HER activity, which is confirmed by means of selective etching of MnOx and infrared spectroscopy. Moreover, the crystal size of CoP phase in the heterostructure is lower than that of the mono-component CoP. Furthermore, the decrease of precursor crystal size will give rise to a decrease in the CoP crystal size of heterostructure. The decline of crystal size results in higher active surface area and greater number of interfaces.

Grain Boundary—A Route to Enhance Electrocatalytic Activity for Hydrogen Evolution Reaction

The electrocatalytic hydrogen evolution reaction (HER) of a given metal catalyst is intrinsically related to its electronic structure, which is difficult to alter for further improvement. Recently, it was discovered that the density of grain boundaries (GBs) is mechanistically of great importance for catalytic activity, implying that GBs are quantitatively correlated with the active sites in the HER. Here, by modeling the atomistic structure of GBs on a Au(110) surface, we find that HER performance is greatly enhanced by Au GBs, suggesting the feasibility of the HER mediated by GBs. The promoted HER performance is due to an increase in the capability of binding adsorbed hydrogen on the sites around GBs. A Au catalyst with a dominantly exposed (110) plane is synthesized, where considerable GBs exist for experimental verification. It is found that HER activity is inherently correlated with the density of the GBs in Au NPs. The improvement in HER activity can be elucidated from the geometrical and electronic points of view; the broken local spatial symmetry near a GB causes a decrease in the coordination numbers of the surface sites and the shift up of the d–band center, thereby reducing the limiting potential for each proton−electron transfer step. Our finding represents a promising means to further improve the HER activity of a catalyst.

Enhancement of hydrogen evolution reaction kinetics in alkaline media by fast galvanic displacement of nickel with rhodium – From smooth surfaces to electrodeposited nickel foams

Energy-efficient hydrogen production is one of the key factors for advancing hydrogen-based economy. Alkaline water electrolysis is the main route for the production of high-purity hydrogen, but further improvements of hydrogen evolution reaction (HER) catalysts are still needed. Industrial alkaline electrolysis relies on Ni-based catalysts, and here we describe a drastic improvement of HER activity of Ni in alkaline media using several model catalysts for HER, obtained upon nickel surface modification in the aqueous solution of rhodium salts, where a spontaneous deposition of rhodium takes place, based on the chemical displacement reaction 3Ni + 2Rh3+ = 3Ni2+ + 2Rh. In the case of smooth Ni-poly electrodes, HER activity surpasses the activity of Pt-poly after just 30 s of exchange with Rh. SEM analysis showed that Rh is uniformly distributed, and that surface roughness changes are lower than 10%, which is in agreement with the electrochemical measurements. Furthermore, XPS analysis has shown effective incorporation of Rh in the surface, while DFT calculations suggest that hydrogen binding is significantly weakened on the Rh-modified Ni surfaces. Such tuning of the hydrogen binding energy is seen as the main factor governing HER activity improvements. The same galvanic displacement protocols were employed for nickel foam electrodes and electrodeposited Ni on Ti mesh. In both cases, somewhat longer Rh exchange times are needed to obtain superior activities than for the smooth Ni surface, but within 10 min. HER overpotentials corresponding to −10 mA cm−2 for nickel foam and electrodeposited Ni electrodes, after modification with Rh, amounted to only −0.07 and −0.09 V, respectively. Thus, it is suggested that a fast spontaneous displacement of Ni with Rh could effectively boost HER in alkaline media with minor cost penalties with regards to energy saving in the electrolysis process.

Twinning Enhances Efficiencies of Metallic Catalysts toward Electrolytic Water Splitting

AbstractTwinning is demonstrated to be an effective way of enhancing efficiencies of metallic catalysts toward electrolytic water splitting. Dendritic Cu possessing dense coherent nanotwin (NT) boundaries (NTCu‐5nm) is successfully prepared with an organic‐assisted electrodeposition at high pulse current densities. NT boundaries significantly improve electrocatalytic efficiencies and stability of NTCu‐5nm over nanocrystalline Cu (NCCu), reducing overpotentials at 10 mA cm−2 for the oxygen evolution reaction (OER) from 378 to 281 mV and from 235 to 88 mV for the hydrogen evolution reaction (HER), with a small chronoamperometric decay of 5% after 100 h continuous overall water splitting at an ultrahigh initial current density of 500 mA cm−2, largely outperforming the large chronoamperometric decay of 27% for only 1 h operation of the NCCu//NCCu couple. The defective twin boundaries enable formation of active CuIIIO2− at low overpotentials, thus enhancing OER performance. The synergistic geometric and electronic effects induced by the twin boundaries result in shifts in Gibbs free energies of hydrogen adsorption (ΔGH) toward the apex of a volcano plot of exchange current density versus ΔGH, leading to the remarkable improvement in HER activity.

Boosting the HER electrocatalytic activity over RuCu-supported carbon nanosheets as efficient pH-independent catalysts

Electrochemical water splitting to produce hydrogen is a key technology for converting sustainable energy into chemical fuels. The high overpotential and sluggish kinetics for the electrocatalytic hydrogen evolution reaction (HER) lead to low energy conversion efficiency. Herein, we report a new electrocatalyst of RuCu supported on guanine-derived carbon nanosheets for highly efficient HER, in which the trace Cu of 0.1 wt% loadings can significantly boost the electrocatalytic activity during the whole pH range. Specifically, the 0.5Ru0.1Cu-GN1000 can release a current density of 10 mA/cm2 at 68 mV and 157 mV in 1.0 M KOH and 0.5 M H2SO4, respectively. This catalyst still delivers a high HER activity even in the actual seawater. The improvement of HER activity can be ascribed to the strong interaction between Ru and Cu, resulting in the formation of an electron-rich state of Ru nanoparticles at the surface for series of HER at low overpotential. This research has opened up a promising pathway towards electrocatalytic water splitting through the innovation of carbon support and the modulation of metal interactions.

PtRu alloy nanoparticles embedded on C2N nanosheets for efficient hydrogen evolution reaction in both acidic and alkaline solutions

Designing a highly efficient and low-cost electrocatalyst for hydrogen evolution reaction (HER) is of great importance to produce high-purity hydrogen, yet it still remains a huge challenge. Here, we present a facile synthesis of this electrocatalyst, PtRu alloy nanoparticles supported on C2N nanosheets, using a condensation-reduction approach. The PtRu@C2N exhibits comparable performance than the commercial Pt/C and higher efficiency than monometallic Pt@C2N and Ru@C2N in both acidic and alkaline conditions. The highly enhanced activity and fast kinetics of PtRu@C2N were attributed to the large electrochemical active surface area, unique electronic structure of PtRu nanoparticles on C2N nanosheets. Density functional theory calculations show that the alloy effect and the metal-support interaction in PtRu@C2N catalyst optimizes the adsorption energy of H atom and other intermediates, resulting in the improvement of HER activity.

Pt-decorated fluorine-free Ti3C2TX for hydrogen evolution reaction

Carbon support in commercial Pt/C suffers severe corrosion in harsh electro-oxidation environments caused by anode potentials. Alternative support should be developed to improve the quality, activity, and durability of platinum by studying the relationship between platinum and support. Here, we prepare fluorine-free Ti3C2TX (T = –OH, –O) powder via a sodium hydroxide etching process to fix Pt nanoparticles. The resulting fluorine-free Ti3C2TX/Pt composite features stable layered structure and metallic properties. As an electrocatalyst for hydrogen evolution reaction (HER), the overpotential of fluorine-free Ti3C2TX/Pt in a 0.5 M H2SO4 water solution at − 10 mA/cm−2 is only 180 mV and 25% lower than that of fluorine-containing Ti3C2TX/Pt. The HER performance remains stable after 80 h of reaction. The improvement in HER activity of the fluorine-free Ti3C2TX/Pt can be attributed to the excellent electrical conductivity, more active sites, less inert surface groups, and electronic effects between the Pt and surface functional groups of alkali-etched Ti3C2TX. This work broadens the application of fluorine-free Ti3C2TX in the field of hydrogen evolution reactions.

Manipulation of Electron Transfer between Pd and TiO2 for Improved Electrocatalytic Hydrogen Evolution Reaction Performance.

The urgent need of catalysts with improved performances toward the hydrogen evolution reaction (HER) is still one of the crucial issues for the water splitting electrocatalysis. Herein, we exhibit that the HER activity of the Pd nanocubes could be improved by selecting the appropriately shaped titania nanocrystals as support. In particular, we used Pd nanoparticles with (100)-facet exposed to show that the HER performance of Pd cubes can be improved in both acidic and alkaline electrolyte media when combined on the anatase TiO2 nanocrystals. Furthermore, we have also investigated the facet effect of TiO2 on the performance in detail, which indicated stronger catalytic activity when (001)-TiO2 was used rather than (mix 101/001)-TiO2 and (101)-TiO2. The electron-transfer-induced improvement of HER activity of Pd/TiO2 was assessed by electron energy loss spectroscopy (EELS). Thereafter, the combined support materials with suitable facet exposed can give an additional adjusting path to regulate the HER activities of Pd nanocatalysts, which henceforth can further contribute to a novel way for tuning other catalysts with good electrocatalytic properties.

Flame-like Ni(OH)2 strongly promotes the dissociation of water and can be used to produce an excellent hybrid electrocatalyst for the hydrogen evolution reaction in alkaline media

In this communication, Ni(OH)2 with a flame-like morphology was successfully electrodeposited on nickel foam (NF) using a ZnO buffer layer. The flame-like Ni(OH)2/NF exhibited efficient activity for the hydrogen evolution reaction (HER) in alkaline media, requiring overpotentials of only 56.4 and 115.8 mV to reach current densities of 10 and 100 mA cm−2, respectively, with a low Tafel slope of 52.8 mV dec−1. These results are nearly comparable to those of commercial Pt/C. The significant improvement in HER activity could be attributed to the flame-like morphology of Ni(OH)2, which may strongly promote the dissociation of water and accelerate the formation of Had. This work also provides a new approach to designing efficient hybrid catalysts for the hydrogen evolution in alkaline media.

Co-W/CeO2 composite coatings for highly active electrocatalysis of hydrogen evolution reaction

Co-W/CeO2 composite coatings were electrodeposited under galvanostatic conditions from a citrate plating bath containing suspended micro-CeO2 particles. The composition, structure and morphology of the composite coatings were evaluated and compared when different concentrations of micro-CeO2 particles are added. The as-prepared Co-W coating without CeO2 has an amorphous structure. However, embedding CeO2 into the Co-W matrix considerably improved the crystallinity of the Co-W alloy. The surface morphology study revealed that Co-W/CeO2 composite coatings were more compact with fewer microcracks and defects than the Co-W coating. The electrocatalytic performance of these composite coatings for hydrogen evolution reaction (HER) was also investigated by liner sweep voltammetry and electrochemical impedance spectroscopy techniques in alkaline medium. Co-W/CeO2 composite coatings gained remarkable improvement in HER activity which may be attributed to a synergistic eletrocatalytic effect between CeO2 particles and Co-W matrix. The apparent exchange current density value (j0) of the Co-W/CeO2 composite coating was 15.6 times higher than that of the Co-W coating when the concentration of micro-CeO2 particles in the plating bath is 7 gL-1 (denoted as M3), and the j0/Rf ratio (intrinsic catalytic activity) was 3.72 × 10−5 Acm−2. Furthermore, M3 coating also showed good stability and its apparent activation energy (Ea) of HER was calculated to be 24.59 kJmol-1, which was significantly lower than that of the Co-W coating.

Improved HER activity of Ni and stainless steel electrodes activated by NiCoMo ionic activator – A combined DFT and experimental study

In this paper we discussed various factors contributing to the improvement of hydrogen evolution reaction (HER) activity of Ni and stainless steel electrodes activated by in situ addition of NiCoMo activators, using a combination of experimental techniques and DFT calculations. By comparing energy consumption of stainless steel (SS) electrodes in a lab scale alkaline electrolyzer with and without ionic activation, we obtained reduction of energy consumption by 21% at industrial conditions (high current density and temperature). We recorded U–I curves for activated and non-activated stainless steel electrodes in the current density range from 40 to 500 mA cm2 and in the temperature range 298–343 K, and the obtained results were used in an electrochemical model of the laboratory alkaline electrolyzer. Increase of the electrode surface upon addition of ionic activators was confirmed by profilometric measurements and SEM analysis. Finally, we applied density functional theory (DFT) to discuss partial roles of applied ionic activators (Ni, Co and Mo) in the modification and improvement of the intrinsic properties of the cathode towards the HER in alkaline medium. From the combination of profilometric, SEM and DFT results, we conclude that the main factor contributing to the improvement of HER activity of Ni electrodes upon NiCoMo activation is the increase of electrode surface area.

3D multi-structural porous NiAg films with nanoarchitecture walls: high catalytic activity and stability for hydrogen evolution reaction

The design of efficient and stable electrocatalysts for hydrogen evolution reaction (HER) is essential to the sustainable hydrogen production by water electrolysis. The catalytic activity of electrocatalysts can be significantly improved by increasing the effective active area. The 3D multi-structural micro/nanoporous NiAg films with nanoarchitecture walls were directly electrodeposited by hydrogen bubble template method. The catalytic activity and durability of NiAg films for HER were studied in 6M KOH solution based on the adjustment of the surface roughness and the wettability. It was found that the walls of porous NiAg films were composed of nanoparticles and nanochannels. However, the closely arranged microparticles were only observed in the pore walls of Ni films. The thicknesses of NiAg films (>20μm) were much larger than those of Ni (7μm) and Ag film (4μm). The 3D multi-structural porous NiAg films exhibited better catalytic activity than Ni or Ag film. HER on all films was controlled by the electrochemical adsorption step of hydrogen atoms (H) to form MHads. The surface roughness of NiAg films was up to 4352 and much higher than those (32 and 273) of Ni and Ag films. Therefore, the effective active areas for H adsorption on NiAg films increased, which led to the improvement of HER activity. In addition, NiAg films possessed good long-term durability. The cell voltages of water electrolysis on NiAg films were much lower than those on Ni and Ag films. It was ascribed to high catalytic activity and rapid bubble separation on 3D micro/nanoporous NiAg films.

Preparation and Study of thin Films of Tungsten Selenides for Electrocatalytic Hydrogen Evolution

Thin films of tungsten selenides (WSex) were obtained by using a method of shadow-masked pulsed laser deposition. The deposition at room temperature of substrates caused the formation of Se-enriched amorphous films (Se/W∼5) with pronounced surface roughness because of an effective nanoparticle growth. Heating or DC biasing the substrate during the deposition modified the film composition (Se/W∼1.7 – 4) and resulted in the smoothing of the film surface. Annealing the films, deposited at room temperature, as well as heating the substrate during the deposition caused crystallization of the films. Catalytic activity of WSex thin films in hydrogen evolution reaction (HER) was studied in 0.5M H2SO4 aqueous solution at room temperature. The structural state and the chemical composition of WSex films had an expressed impact on the catalytic activity. A significant improvement in HER activity was observed in the case of Se-enriched films deposition followed by annealing at 500°C.