Hydrogen Evolution Reaction Reaction Research Articles

Improving NiFe Electrocatalysts through Fluorination-Driven Rearrangements for Neutral Water Electrolysis.

Neutral electrolysis to produce hydrogen is prime challenging owing to the sluggish kinetics of water dissociation for the electrochemical reduction of water to molecular hydrogen. An ion-enriched electrode/electrolyte interface for electrocatalytic reactions can efficiently obtain a stable electrolysis system. Herein, we found that interfacial accumulated fluoride ions and the anchored Pt single atoms/nanoparticles in catalysts can improve hydrogen evolution reaction (HER) activity of NiFe-based hydroxide catalysts, prolonging the operating stability at high current density in neutral conditions. NiFe hydroxide electrode obtains an outstanding performance of 1000mA cm-2 at low overpotential of 218mV with 1000 h operation at 100mA cm-2. Electrochemical experiments and theoretical calculations have demonstrated that the interfacial fluoride contributes to promote the adsorption of Pt to proton for sustaining a large current density at low potential, while the Pt single atoms/nanoparticles provide H adsorption sites. The synergy effect of F and Pt species promotes the formation of Pt─H and F─H bonds, which accelerate the adsorption and dissociation process of H2O and promote the HER reaction with a long-term durability in neutral conditions.

XPS Analysis of FexNiyPS3 vdW Materials Used in the Hydrogen Evolution Processes.

In response to the global demand for sustainable energy solutions, the quest for stable and cost-effective hydrogen production has garnered significant attention in recent decades. Here, the emergence of layered metal phosphorus trichalcogenides (MPX3, M: transition metal, X: chalcogen) materials and their two-dimensional counterparts with customizable composition and electronic structure holds great promise for such purposes. In the present study, we successfully synthesized large-scale and high-quality FePS3, NiPS3, and an alloyed counterpart, Fe0.5Ni0.5PS3. Subsequent systematic investigations were conducted to probe their respective electronic structures and assess their hydrogen evolution reaction (HER) properties. Remarkably, our results unveiled the successful modulation of the bandgap for FexNiyPS3, ultimately bestowing it with the most favorable HER performance for Fe0.5Ni0.5PS3 when compared to the other two samples. Furthermore, our exploration into the evolution of the X-ray photoelectron spectroscopy (XPS) spectra demonstrated that the charge conversions of metal cations play a pivotal role in the HER reactions. This critical insight further enriches our understanding of the fundamental mechanisms governing the performance of the prepared layered MPX3-based electrocatalysts, thus facilitating a comprehensive and detailed analysis of the pre- and post-HER reactions. This work not only sheds light on the intricate interplay between composition, electronic structure, and catalytic performance in the realm of novel electrocatalysts, but also contributes to the broader scientific community's pursuit of sustainable and efficient hydrogen production.

Regulating lattice tensile strain of Ru-Co bimetallic nanoparticles on carbonized wood for boosting its hydrogen evolution reaction

The development of high-performance catalysts for hydrogen production originating from water electrolysis at the cathode is very crucial, but still a challenge. Here, trace Ru-doped Co bimetallic nanoparticles (named RuxCoy/CW-z, x/y and z represent the molar ratio and total molar content of metals) were in situ decorated on carbonized wood by the vacuum impregnation and high-temperature annealing method. Ru1Co10/CW-2 demonstrates good hydrogen evolution reaction (HER) intrinsic activity with the overpotential of −42 mV (at −10 mA/cm−2) and Tafel slope of 75 mV dec−1 in a 1.0 M KOH, indicating its favorable HER reaction kinetics, and Ru1Co10/CW-2 exhibits good stability for 100 h (at −50 mA/cm−2). The good performances of Ru1Co10/CW-2 can be ascribed to the adjustable lattice tensile strain and electronic interactions, while the porous carbonized wood promotes electron transfer, electrolyte transport and gas escape. This work combines the advantages of lattice tensile strain with self-supported porous carbonized wood for HER in alkaline solution, which provides a valuable reference for synthesizing carbonized wood electrode materials with very low Ru content.

Enhanced Alkaline Hydrogen Evolution Reaction via Electronic Structure Regulation: Activating PtRh with Rare Earth Tm Alloying.

Developing high-performance electrocatalysts for alkaline hydrogen evolution reaction (HER) is crucial for producing green hydrogen, yet it remains challenging due to the sluggish kinetics in alkaline environments. Pt is located near the peak of HER volcano plot, owing to its exceptional performance in hydrogen adsorption and desorption, and Rh plays an important role in H2O dissociation. Lanthanides (Ln) are commonly used to modulate the electronic structure of materials and further influence the adsorption/desorption of reactants, intermediates, and products, and noble metal-Ln alloys are recognized as effective platforms where Ln elements regulate the catalytic properties of noble metals. Here Pt1.5Rh1.5Tm alloy is synthesized using the sodium vapor reduction method. This alloy demonstrates superior catalytic activity, being 4.4 and 6.6 times more effective than Pt/C and Rh/C, respectively. Density Functional Theory (DFT) calculations reveal that the upshift of d-band center and the charge transfer induced by alloying promote adsorption and dissociation of H2O, making Pt1.5Rh1.5Tm alloy more favorable for the alkaline HER reaction, both kinetically and thermodynamically.

Facile fabrication of MoS2 and MoSe2 layered structures on Mo foil for the efficient photocatalytic dye degradation and electrocatalytic hydrogen evolution reaction

The rapidly growing necessity for sustainable materials in fields such as energy, environmental science, and medicine, two dimensional-based photo- and electro-catalysts has obtained mounting consideration. A simple methodology was employed to fabricate MoSe2 and MoS2 layered structures on flexible Mo foil as heterogeneous catalysts for the electrocatalytic hydrogen evolution reaction (HER) and the photocatalytic decolorization of chromic red (CR) and methylene blue (MB) dyes. The structural characteristics confirm the formation of the multi-layer thick MoSe2 and MoS2 nanofilms. The toxic MB and CR dyes were rapidly and effectively decolorized in polluted water by the photocatalysts within 30 min of UV-light irradiation. The fabricated layered structures exhibited favorable HER electrocatalytic activities along with low overpotentials, small Tafel slopes, and excellent 24-h stability performances. The strong catalytic behavior of these structures fabricated on Mo foil in relation to the HER reaction and the dye decolorization process make them suitable candidates for the catalyst industry.

Fluorination of porphyrin β-periphery boosts nickel(II)-catalyzed hydrogen evolution reaction

Tunichlorin, the naturally occurring chlorophyll cofactor containing Ni(II) ion, sets up a golden standard for designing the electrocatalysts for hydrogen evolution reaction (HER) via β-peripheral modification. Besides the fine-tuning of the porphyrin β-periphery such as adjusting the aromatics (the saturated level of tetrapyrrole) or installing hydroxyl group (hydrogen bond network) to enhance the catalytic HER efficiency, here we report that β-fluorination of porphyrin is also an important approach to increase the reactivity of Ni(II) center. Benefiting the previously reported derivatization of β-fluorinated porpholactones, we constructed a β-fluorinated tunichlorin mimic (6). Compared with the non-fluorinated analogs (1, 3, and 5), we found that 2, 4, and 6 exhibit significant electrocatalytic HER reactivity acceleration (in terms of turnover frequencies, TOF, s−1) of ca. 37, 170, 133-fold, respectively. Mechanism studies suggested that β-fluorination negatively shifts the metal complexes' reduction potentials and accelerates the electron transfer process, both contributing to the boosting of HER reaction. Notably, 6 showed an 890-fold increase of TOFs than 1, demonstrating the combining advantages of the of fluorination, hydrogenation, and hydroxylation at porphyrin β-periphery.

Two-dimensional Janus AgBiP2X3X[formula omitted] (X, X[formula omitted] = S, Se, Te): Efficient intrinsic electric field regulatory strategy for photocatalytic overall water-splitting

Exploring highly efficient catalysts that utilize visible light for water-splitting shows immense potential in addressing energy and environmental challenges. However, most photocatalysts are faced with challenges such as low carrier migration ability, high carrier recombination rate, and insufficient driving force for water-splitting reactions. Here, based on the two-dimensional (2D) AgBiP2X6 (X = S, Se, Te) structures, we construct Janus AgBiP2X3X3′ (X, X′ = S, Se, Te) monolayers and theoretically investigate their photocatalytic performance. The results indicate that the Janus method effectively regulate the energy band structure and intrinsic electric field (EF) of the materials. The Janus AgBiP2S3Te3 structure possesses an optimal band gap and band edge position in comparison to AgBiP2X6. Among all the investigated materials, AgBiP2S3Te3 possesses the largest intrinsic EF. The vertical intrinsic EF in Janus AgBiP2S3Te3 facilitates spatial separation of photogenerated electrons and holes, allowing hydrogen evolution reaction (HER) to take place on its top surface and oxygen evolution reaction (OER) to occur on its bottom surface, thereby effectively preventing carrier recombination. The limiting potentials for OER and HER reactions are significantly reduced. The OER can proceeds spontaneously under neutral conditions. The Gibbs free energy change (ΔG) of the HER is 0.075 eV under acidic conditions at pH = 0, which closely approaches the optimal value of 0. Simultaneously, the Janus AgBiP2S3Te3 exhibits kinetic and thermal stability, suitable appfavorableropriate electron and hole mobility, and excellent visible light absorption capability. Our work not only predict a series of new 2D materials, but also paves a strategy for improving the photocatalytic properties of 2D ferroelectric materials.

Can Re cluster complexes be an efficient catalyst for hydrogen evolution reaction? Insights from experiments and computations.

To date, researchers in chase of economic cost-efficiency are faced with the problem of developing effective catalysts for water splitting without the use of platinoids. Herein, catalytic properties of hexanuclear rhenium cluster complexes are investigated in application to the hydrogen evolution reaction (HER). A paste composite electrode containing the cluster complexes was obtained, producing a current density of 10 mA cm-2 at an extraordinarily low overpotential of 90 mV (RHE). The {Re6Se8}-based complexes have shown very favorable reaction kinetics via 102 mV dec-1 value of the Tafel slope for HER reaction within the composition of the paste electrode. Model calculations of kinetic parameters using density functional theory also support the experimental findings. This work underscores the perspectivity of rhenium cluster compounds in HER and opens a promising avenue toward the practical implementation of hydrogen production through electrochemical water splitting.

Decoupled Electrolysis: A Novel Method for Water Splitting Using WO3 Auxiliary Electrode

More emphasis must be placed on the use of clean and renewable energy sources. Production of electricity using solar, wind geothermal etc is becoming more widespread however these types of energy production suffer from intermittence in production and a mismatch of production and consumption cycles. These problems result in a need for an energy storage medium. A hydrogen is a viable option because of its high gravimetric heat capacity (143 MJ/kg) and low flashpoint (-231°C) [1]. For now, most of the produced hydrogen is from hydrocarbons and only 4% is being produced using electrolysis. Hydrogen production via electrolysis is an efficient way how to store surplus energy from renewable energy sources but electrolysis must be made more achievable. Commonly used water electrolysis is limited by the need for complicated gas distribution systems to avoid mixing of H2 and O2 which can lead to a serious safety hazard. Membranes and diaphragms can solve gas mixing problems but they significantly reduce efficiency and increase hydrogen production costs.Here we demonstrate the principle of decoupled electrolysis where oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is separated in space with the use of a WO3 redox mediator. WO3 was produced by the solvothermal method. In accordance with SEM (Fei, NanoSEM 650), XRD (Rigaku, Ultima+) and XPS (Thermo Scientific, Escalab Xi+) data, monoclinic WO3 nanosheet assemblies with a cluster size of 10-20 μm and plate thickness of 50-100 nm were produced without lower oxidation states. Electrodes were produced using carbon felt which was saturated with ink suspension containing active material (WO3), carbon black and polyvinyl difluoride (PVDF) in a mass ratio of 60-30-10. DMF was used as a solvent. Electrolysis was achieved in a two-step process. In the first step, an OER reaction occurs and the H ion is intercalated into WO3 forming tungsten bronze HxWO3. OER reaction occurs on platinum and O2 is released with gas purity above 99.9 %. In the second step, H ion deintercalation occurs and H2 is released at the Pt electrode with a purity greater than 99.9%. Gas purity was determined using a gas mass spectrometer. Electrochemical measurements were performed using Metohm AutoLAB potentiostat with Nova software. The electrode was analysed using cyclic voltammetry (CVP), impedance spectroscopy (EIS) and chronopotentiometry. 0.5 M H2SO4 was used as an electrolyte solution.In accordance with the CVP capacity of the WO3 electrode reaches 325 F/g at a scan rate of 2 mV/s and decreases with an increase in scan speed. A decrease in capacity due to an increase in scanning speed can be associated with limited charge diffusion [2]. The shift of the maximum in the anodic direction associated with the transition from W5+ to W6+ with an increase in scan speed is polynomial and can be associated with the pseudocapacitive behaviour of electrode material. The Nyquist plot from EIS measurements shows the formation of an incomplete arc in the high-frequency interval and linear correlation in lower frequencies. In chronopotentiometry with a current density of 100 mA/g faradaic efficiency reached 90.2% and increased to 100% when 1000 mA/g were used, however taking into account both OER and HER reactions, cycle efficiency decreased from 65 to 43 % with the same current densities. If only HER reaction is analysed when hydrogen is being released and deintercalation happens, cycle efficiency reaches 341 %. High efficiency can be explained by extra energy obtained from the building potential of the WO3 electrode that lowers the standard potential for water electrolysis. Long-term tests showed good stability and no degradation was observed in accordance with SEM and XPS studies. At high intercalation-deintercalation cycle times, a non-Faradaic process can be observed which reduced HER cycle time. A spontaneous deintercalation can be observed. One of the future goals is to prevent this process by the use of different auxiliary electrode materials.[1]-Tashie-Lewis BC, Nnabuife SG. Hydrogen production, distribution, storage and power conversion in a hydrogen economy - a technology review. Chemical Engineering Journal Advances 2021;8:100172.[2]- Das AK, Karan SK, Khatua BB. High energy density ternary composite electrode material based on polyaniline (PANI), molybdenum trioxide (MoO3) and graphene nanoplatelets (GNP) prepared by sonochemical method and their synergistic contributions in superior supercapacitive performance. Electrochim Acta 2015;180:1e15. Figure 1

N-Doped Norbornane sp2 Carbon Framework: An Efficient Electrocatalyst for Oxygen Reduction and Hydrogen Evolution Reaction

At present, development of Pt free bifunctional electrocatalyst for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is necessary for the advancement of sustainable and cost-effective solutions for energy conversion and storage technology. In this direction, herein we report N doped sp2 hybridized carbon framework (N-CF) as a metal-free electrocatalyst for ORR and HER. This work inspects the effect of N doping that converts a hybrid structure of CF {Norbornane or bicyclo [2, 2, 1] heptane structure} into planar N-CF. A series of N-doped CF with different doping concentrations has been prepared using a facile and cost-effective technique. This robust electrocatalysts exhibits a promotional effect in the activity, porosity, thermal and electrochemical stability for the ORR and HER reactions. A rich delocalized electronic density of the sp2 bounded N species helps in modulating antibonding state of molecular oxygen and facilitates the breakage of O=O bond in ORR. It also promotes proton adsorption via bonding between proton and valence electron rich catalyst surface to aid HER. The research sought to investigate the employability of N-CF for fabricating sustainable energy devices with electrocatalyst possessing multiple electrocatalytic activities for ORR and HER. Figure 1

Acenaphthenediimine complex-bridged porphyrin porous organic polymer with enriched active sites as a robust water splitting electrocatalyst

To realize efficient water splitting, a highly promising hydrogen evolution reaction (HER) electrocatalyst is needed for the generation of hydrogen. Herein, we demonstrate a novel acenaphthenediimine complex-bridged porphyrin porous organic polymer (NiTAPP-NiACQ) with enriched active metal sites and hierarchical pores. The as-prepared NiTAPP-NiACQ exhibits good long-term durability and remarkable HER performance in 1.0 M KOH with a low overpotential of 117 mV at 10 mA cm−2, which is comparable to many previously reported electrocatalytic HER systems. Furthermore, a simple water-alkali electrolyzer using NiTAPP-NiACQ as the cathode requires a small cell voltage of 1.59 V to deliver a current density of 10 mA cm−2 at room temperature, along with outstanding durability. NiTAPP-NiACQ features not only a metal ion as the catalytic active center in the porphyrin core but also metal ion coordination on the anthraquinone component to promote HER performance, enabling multiple metal ions as the electrocatalytic active sites for the HER reaction. The excellent HER activity of NiTAPP-NiACQ is ascribed to a combination of mechanisms. These findings highlight the viability of porphyrin-derived porous organic polymers in energy conversion processes.

Enhancing electrocatalytic ammonia synthesis through theoretical design of cluster catalysts supported on TiO2 surface

The electrocatalytic nitrogen reduction reaction (NRR), conducted under ambient conditions, holds promise as a viable alternative to the traditional Haber-Bosch process. However, the progress in developing effective electrocatalysts for NRR is stymied by the intense competition with the hydrogen evolution reaction (HER), which leads to low rates of ammonia yield and Faradaic efficiencies. This challenge can be tackled by utilizing well-defined loaded two-dimensional TiO2 structured model catalysts. In this study, we introduce an efficient Cobalt–Nickel electrocatalyst (Co1Ni2@TiO2) based on theoretical predictions. Through a rational screening of 16 TiO2-based catalysts, we identified Co3, Co1Ni2, and Ni1Mn2@TiO2 as effective suppressors of the HER reaction. Among these, Co1Ni2@TiO2 demonstrated the lowest energy barrier for the potential-determining step, at 0.39 eV. We then experimentally synthesized Co1Ni2@TiO2. This catalyst exhibited a superior yield of 20.396 μgNH3/mgcat/h and a Faradaic efficiency of 13.327 %. This signifies a minimum of 2.9-time enhancement when compared to Co3@TiO2 and Ni3@TiO2.

Surface engineered low-cost paper electrodes for enhanced electrocatalytic activity

Hydrogen evolution reaction (HER) is considered the most promising way to produce clean and sustainable hydrogen energy. Carbon-based materials have been discovered to be efficient for catalyzing HER reactions in addition to conventional noble metal-based electrodes. Surface engineering of electrodes through simple methods are important to enhance the electrochemical properties and to keep the cost economical. Herein, we tried to understand the influence of simple electrochemical pre-treatment methods on Paper electrode (PPE) surface towards electrocatalytical activity. The pretreatment methods involving simple voltametric scanning and pre-anodization has been carried out under various electrolytic conditions and investigated for their role on electrochemical activities. The pretreated electrodes were thoroughly characterized with surface morphological and electrochemical techniques. The pre-anodized disposable paper electrode (PA-PPE- H2SO4) modified with pyrene butyric acid (PA-PPE- H2SO4-PBA) was found to show excellent electrochemical properties and exhibited a low-potential HER (Onset potential, Eonset = -0.1 V Vs. RHE) in 0.5 M H2SO4 with a Tafel slopes, 34.2 and 49.88 mV/ dec−1. The obtained results are substantially better than that of reported carbon-based electrodes, where the benefit of Platinum leaching out from the counter electrodes are speculated. The formation of edge-plane sites/defects, and functional groups on electrode surfaces and modification effect by PBA are the reason behind the increased the electrochemical response. Since paper has been used as a substrate for fabrication of the electrodes, possibility to use the same in future as a flexible current collector for self-powering wearable devices/sensors are anticipated.

Spontaneous hydrogen production on well-designed two-dimensional MoSi2N2P2 Janus structure: N-face versus P-face tuning

Based on the recently discovered two-dimensional non-Janus MoSi2N4 structure, we here study a well-designed two-dimensional Janus structure (MoSi2N2P2) for potential application in hydrogen evolution reaction (HER) via water splitting. We first confirm the stability of the MoSi2N2P2 structure using first-principles’ calculations in the framework of density functional theory by calculating cohesive energy, phonon dispersion, and ab-initio molecular dynamics evolution. We then investigate electronic and transport properties of the structure. The MoSi2N2P2 Janus structure exhibits an indirect (Γ→M) band gap of only 0.22 eV using PBE and 0.89 eV using the HSE06 hybrid functional. We also find that there is a large intrinsic electric field across the Janus structure, which tends to gather electrons at the P face. We also calculate the mobility of the Janus structure, showing that it has a high electron mobility (409 cm2/Vs) along the zigzag direction. We then show that compared with the P face, the N face gives a lower overpotential against HER, but not sufficient to activate HER process. Therefore, we investigate how the electronic properties and the HER overpotential of the Janus MoSi2N2P2 monolayer are affected by applying biaxial strain and external perpendicular electric field. Thus, the N face exhibits a higher degree of tunability than the P face toward HER overpotential. In particular by applying an electric field of 2.7 V/Å directing from the P face to the N face, the overpotential against the HER reaction on the N face can be adjusted to zero, showing that the well-designed Janus structure can exhibit a potential application for spontaneous HER water splitting.

Ni-Ti3C2 MXene composite derived from Ni-metal organic framework for electrochemical hydrogen evolution reaction in acidic and alkaline medium

MOFs derived metal composites are found to be a potential electrocatalyst for energy storage and conversion process. In this work, Ni composite with MXene (Ni-Ti3C2) was synthesized by calcination of Ni-MOF at 650 °C and characterized by XRD, FE-SEM, FTIR and BET analysis. After calcination, the derived Ni composited Ti3C2 showed a high porosity and high surface area as compared to Ti3C2. The derived material was further used as electrode for Hydrogen Evolution Reaction (HER) and tested by various electrochemical analysis viz. Cyclic voltammetry (CV), Electrochemical impedance analysis (EIS) and Linear Sweep Voltammetry (LSV) in alkaline medium. The derived Ni-Ti3C2 in basic medium displays a small Tafel value of 56.15 mV/dec with acquired voltage of 181.15 mV due to the surface area and accessible catalytic active sites, which provides excellent mass transfer properties for derived Ni-Ti3C2 composite in basic medium. The kinetics of the HER reaction was found better in Ni-Ti3C2 MXene composite in basic medium than in acidic medium. The charge transfer resistances were obtained from the EIS plot and were found to be 3.98 Ω and 2.34 Ω for Ti3C2 and Ni-Ti3C2 respectively in acidic medium and 3.12 Ω and 1.98 Ω in basic medium. The low resistance observed for Ni-Ti3C2 in basic medium proves a higher electrocatalytic activity in Ni-Ti3C2 than Ti3C2. The cyclic stability of the Ni-Ti3C2 in basic medium was higher than Ti3C2. Thus the overall results show that the prepared composite is a potential catalyst for HER applications.

Working mechanism of MXene as the anode protection layer of aqueous zinc-ion batteries

In recent years, the research on intrinsically safe aqueous zinc-ion batteries (AZIBs) has gained significant attention. However, the commercialization of AZIBs is hindered because of the formation of dendrites in them and undesired hydrogen evolution reaction (HER) at their anode. MXene is a promising two-dimensional material that can inhibit dendrite growth and undesired HER at the anode when used as a protective layer for the anode in AZIBs. MXene’s surface functional groups play a crucial role in this protective function. However, the working mechanisms of these surface functional groups have not been thoroughly understood. Based on first-principles calculations and molecular dynamics simulation, we investigated the mechanisms of MXene with nine surface functional groups, including oxygen and halogen elements, as an anode protection layer. We checked their structural stability, electronic structure, adsorption energy, HER reaction free energy, Zn2+ diffusion energy barriers, coordination number of Zn2+- H2O and diffusion coefficients of Zn2+. The MXene species with -S and -O functional groups exhibit good electrical conductivity and greatly adsorb Zn2+. Conversely, MXene species with halogen-functional groups significantly inhibit HER reactions. MXene materials with -Se functional group have the best desolvation effect (ΔCN = 0.31), while those with -I end group have the fastest ability to diffuse zinc ion. This research provides a theoretical guidance for the design of MXene based anode protection layers, which can help to develop dendrite-free and low side-reaction AZIBs.

Structural properties and hydrogen evolution reactions of predicted two-dimensional V n C n (n = 2, 3, 6) with first-principles calculations

Developing stable, conductive and effective nonprecious hydrogen evolution reaction (HER) catalysts is critical to the future of the hydrogen economy. The possible structures of the two dimensional V n C n were searched with the evolutionary algorithm associated with the density functional theory (DFT) calculations. V n C n (n = 2, 3, 6) were found stable and the structures were refined with the DFT-PBE approaches at higher computational accuracies. Their thermal, dynamical and mechanical stabilities were confirmed theoretically with the same method. The electronic and the HER catalytic properties of these structures were investigated. All the structures exhibit metallicity, which is favorable to support adsorbing hydrogen atoms and transferring charges during HER. The Gibbs free energy of HER reactions support that the 2D V n C n (n = 3, 6) possess the catalytic ability of HER.

Plasma-assisted in situ engineering of bimetallic phosphate coated Ni(OH)2–CuO nanosheets for robust electrocatalytic hydrogen evolution

Hydrogen production by water electrolysis is a promising green and sustainable energy source, and engineering low-cost and high-efficiency electrocatalysts is crucial to ensure reliable and abundant global energy supply. Herein, a new and effective approach for electrocatalyst production for robust hydrogen evolution reaction (HER) is reported. The Ni–Cu hydroxide and oxide nanosheets are directly synthesized on the plasma-treated nickel foam (PNF) substrate, and then the ultrathin layer of transition metal phosphate is electrodeposited. The CuO and Ni(OH)2 heterostructures effectively enrich the catalytically active sites, reduce the HER free energy while greatly increasing the conductivity, thus causing the high HER activity. Meanwhile, the multilayer nickel-cobalt phosphate not only accelerates the HER reaction kinetics, but also acts as a protective layer, which greatly improves the electrode stability. The overpotential of the synthesized NiCo–P@CuO–Ni(OH)2/PNF catalyst is 59 mV (Tafel slope is 51.4 mV dec−1) for HER driven with a current density of 10 mA cm−2 (j10) in 1.0 M KOH electrolyte. Importantly, the nanostructure and sustainable activity of NiCo–P@CuO–Ni(OH)2 are retained after a 100 h HER process under the simulated industrial conditions. The Density Functional Theory and in situ Raman results reveal that the nickel sites exposed at the CuO–Ni(OH)2 heterointerface act as the HER catalytically active centers.

Preparation of carbon sponge loaded NiPt dual-metal single atom as self-supporting electrode based on inkjet printing technology for efficient hydrogen evolution

Hitherto, Pt-based catalysts still occupy a dominant position in hydrogen evolution reaction (HER), but high cost greatly restricts their applications. Dual metal-atom catalysts (DACs) break the limitation of symmetrical charge distribution at single atomic sites, leading to the synergistic effect to reduce adsorption energies of reaction intermediates by optimized electronic structure. Herein, ZIF-8 derived strategy by inkjet printing is proposed to prepare NiPt dual-metal single atom in situ on porous carbon sponges (NiPt/CMS) as HER self-supporting electrodes. Inkjet printing is helpful to avoid aggregation of nanoparticles, so that resulting in high atomic sites density of the self-supporting electrode. Based on this, the interaction between Ni and Pt atoms of NiPt/CMS catalyst results in faster charge transfer and moderate binding with intermediates, promoting the catalytic activity of HER reaction is improved. As a result, overpotentials of 66 mV in acidic media and 67 mV in alkaline media at the current density of 10 mA cm−2 are reported for NiPt/CMS, highlighting the dual-metal single atom effect. This work provides inspiration for multiple active sites in SACs.

G-C3N4/Chlorocobaloxime Nanocomposites as Multifunctional Electrocatalysts for Water Splitting and Energy Storage.

Due to environmental contamination and the depletion of energy supplies, it is very important to develop low-cost, high-performance, multifunctional electrocatalysts for energy conversion and storage systems. Herein, we report the development of cost-effective modified electrodes containing g-C3N4/chlorocobaloxime composites (C1-C4) and their electrocatalytic behavior toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), followed by their energy-storage applications. A series of chlorocobaloximes {ClCo(dpgH)2B} with diphenylglyoxime (dpgH) and neutral bases (B) containing a carboxylic acid moiety (isonicotinic acid, pyridine-3,5-dicarboxylic acid, indole-2-carboxylic acid, and p-aminobenzoic acid) have been synthesized and characterized by spectroscopic techniques. The nanocomposites of g-C3N4/chlorocobaloximes are prepared and characterized by Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray photoelectron spectroscopy (XPS), particle size distribution analysis (PSA), Brunauer-Emmett-Teller (BET), and energy dispersive X-ray analysis (EDAX) techniques. The composite coatings exhibit enhanced HER performance at lower overpotential and with a lower Tafel slope. When the water-splitting reactions are studied using 0.5 M H2SO4 and 0.5 M KOH as electrolytic solutions, the composite g-C3N4/C2 containing pyridine-3,5-dicarboxylic acid as a neutral base shows excellent HER activity with a lower overpotential of 173 mV at -10 mA cm-2 and OER activity with a lower overpotential of 303 mV. The HER reaction takes place through the Volmer-Heyrovský mechanism, where the desorption step is the rate-determining step. Among the synthesized nanocomposites, the nanocomposite g-C3N4/C2 shows higher efficiency toward both HER and OER reactions, with a lower Tafel slope of 55 mV dec-1 for HER and 114 mV dec-1 for OER than the other nanocomposites. The overall water-splitting studies of the composite g-C3N4/C2 in 0.5 M KOH indicate that the evolution of hydrogen and oxygen occurs constantly up to 120 h. The supercapacitance applications studied using cyclic voltammetry and charge-discharge studies indicate that the nanocomposite g-C3N4/C1 shows a good specific capacitance of 236 F g-1 at 0.5 A g-1 compared to others. The increased electrochemical performance of the synthesized nanocomposites is due to the incorporation of electron-withdrawing carboxylic-acid-functionalized neutral bases present in cobaloximes, which increases electron mobility. The incorporation of a cobaloxime complex into a g-C3N4 nanosheet enhances the electrocatalytic behavior of the nanosheet, and its performance can further be fine-tuned by systematic variation in the structure of cobaloxime by changing the halide ion, dioxime, the neutral base ligand, or the substituent.