Enhanced Hydrogen Evolution Reaction Performance Research Articles

Synthesis of nitrogen and sulfur bi-doped carbon obtained from spent sapelli wood sawdust and polyhydric alcohol with improved catalytic activity for hydrogen evolution reaction

Developing an efficient water electrolysis system is an important solution for on the development of highly active, cost-effective, and stable electrocatalysts. Carbon-based metal-free catalysts are one of the promising candidates for this purpose. Herein, we present a facile strategy to synthesize and characterize nitrogen and sulfur co-doped porous carbon (NS-PC) from spent sapelli wood sawdust and polyhydric alcohol (xylitol) for efficient hydrogen evolution reaction (HER) in alkaline electrolyte. The resultant NS-PC metal-free catalyst exhibits porous structure, high surface areas and enhanced HER performance with lowest Tafel slope of 68.1 mV dec−1. The enhanced performance is due to the high porosity of carbonaceous material and co-existence of active species (N in the forms of graphitic-N, pyridinic-N, pyrrolic-N, and S in the forms of C–S–C) induced by the maximum carbon-carbon bond polarization, charge re-distribution in the carbon matrices with a synergistically HER activity. In addition, this work provides a versatile and effective strategy for synthetizing excellent carbon-based metal free catalysts from the low cost biowaste for large-scale production of hydrogen through HER.

Tuning the morphology and crystal phase of Ru nanocatalysts for efficient hydrogen evolution

Regulation of crystal phase of Ru nanocatalysts has been identified as an effective approach in regulating the bonding strength of reaction intermediates to Ru and improving the intrinsic activity of Ru-based catalysts during electrocatalytic hydrogen evolution reaction (HER). Here, we reported that the morphology and crystal phase of Ru nanocatalysts could be facilely regulated by halide anions in hydrothermal synthesis. Structural characterization revealed that halogen anions directed the anisotropic growth of hcp Ru, stabilized Ru crystals from aggregation, and increased the abundance of grain boundaries. As a result, The Ru polycrystalline networks exhibited excellent HER activity and durability with a smaller Tafel slope of 21 mV dec−1 and overpotential (η50) of 18 mV. This work sheds light on the shape and phase control of nanocrystals and future design of high-efficient non-Pt electrocatalysts with enhanced HER performance.

Unraveling the potential of transition metals as single atom catalyst in Graphene/WS2 van der Waals heterostructure for enhanced HER performance – A first principles study

Hydrogen, renowned for its abundance and versatility, stands as a significant green energy alternative, especially when produced through water electrolysis. In this study, 2D/2D van der Waals heterostructure with graphene and WS2 monolayer (GW) is constructed as electrocatalyst for hydrogen evolution reaction (HER). The cohesive energy and the binding energy per area for the GW heterostructure are found to be −0.39 eV and −18.9 meV/Å2 which confirms the structural stability as well as the weak binding of two monolayers. Furthermore, ten 3d transition metals are introduced as single atom catalyst (SAC) in the GW heterostructure (TM@GW) to enhance the catalytic performance. The ΔGH* for all TM@GW shows that there is an enrichment in the HER performance by 47–96 % upon the introduction of SAC, showcasing the superiority of Zn@GW heterostructure with an overpotential of 80 mV and the lowest kinetic barrier of 0.51 eV for the Volmer-Tafel reaction. This investigation provides valuable insight for modeling both van der Waals heterostructures and SACs to enrich catalytic performance.

Breaking Symmetry: Enhanced Hydrogen Evolution Reaction Performance of Janus Zr2COT (T = F, Cl, Br, I) MXenes by Density Functional Theory

Breaking Symmetry: Enhanced Hydrogen Evolution Reaction Performance of Janus Zr₂COT (T = F, Cl, Br, I) MXenes by Density Functional Theory

Hydrogen spillover in Pt/Ni(OH)2/Mo2TiC2Tx electrocatalyst improves pH-universal hydrogen evolution reaction

Electrocatalytic hydrogen evolution reaction (HER) shows potential to transition from fossil fuels to green renewable energy. Designed for high efficiency and stability electrocatalyst in pH-universal electrolyte is of great significance but challenging. Herein, a novel electrocatalyst of two-dimensional (2D) Mo2TiC2Tx MXene supported Pt/Ni(OH)2 (denoted as Pt/Ni(OH)2/Mo2TiC2Tx) is reported by hydrogen spillover effect for efficient HER in the full-pH range. The operando electrochemical characterization reveals that the hydrogen spillover phenomenon interactions between multi-functional catalytic sites, e.g. Pt, Ni(OH)2 and Mo2TiC2Tx, are used to enhance HER performance and expedite HER kinetics. Moreover, theoretical calculation via density functional theory demonstrates the Pt/Ni(OH)2/Mo2TiC2Tx possess free energy of absorbed hydrogen close to zero (≈– 0.09 eV), which leads to optimal activity. As expected, the electrocatalyst necessitates the overpotential of 25, 33 and 36 mV at 10 mA cm−2 in acidic, alkaline, and neutral conditions, respectively, which are outperforming Pt/C. This work furtherly demonstrates a new way to design a powerful electrocatalyst for pH-universal HER based hydrogen spillover phenomenon.

In Situ Growth of Interfacially Nanoengineered 2D-2D WS2/Ti3C2Tx MXene for the Enhanced Performance of Hydrogen Evolution Reactions.

In line with current research goals involving water splitting for hydrogen production, this work aims to develop a noble-metal-free electrocatalyst for a superior hydrogen evolution reaction (HER). A single-step interfacial activation of Ti3C2Tx MXene layers was employed by uniformly growing embedded WS2 two-dimensional (2D) nanopetal-like sheets through a facile solvothermal method. We exploited the interactions between WS2 nanopetals and Ti3C2Tx nanolayers to enhance HER performance. A much safer method was adopted to synthesize the base material, Ti3C2Tx MXene, by etching its MAX phase through mild in situ HF formation. Consequently, WS2 nanopetals were grown between the MXene layers and on edges in a one-step solvothermal method, resulting in a 2D-2D nanocomposite with enhanced interactions between WS2 and Ti3C2Tx MXene. The resulting 2D-2D nanocomposite was thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses before being utilized as working electrodes for HER application. Among various loadings of WS2 into MXene, the 5% WS2-Ti3C2Tx MXene sample exhibited the best activity toward HER, with a low overpotential value of 66.0 mV at a current density of -10 mA cm-2 in a 1 M KOH electrolyte and a remarkable Tafel slope of 46.7 mV·dec-1. The intercalation of 2D WS2 nanopetals enhances active sites for hydrogen adsorption, promotes charge transfer, and helps attain an electrochemical stability of 50 h, boosting HER reduction potential. Furthermore, theoretical calculations confirmed that 2D-2D interactions between 1T/2H-WS2 and Ti3C2Tx MXene realign the active centers for HER, thereby reducing the overpotential barrier.

Innovative Catalyst Design of Sea-Urchin-like NiCoP Nanoneedle Arrays Supported on N-Doped Carbon Nanospheres for Enhanced HER Performance.

Hydrogen (H2) stands as a clean energy alternative to fossil fuels, especially within the domain of the hydrogen evolution reaction (HER), offering prospective solutions to mitigate both environmental and energy-related challenges. In this work, we successfully synthesized a sea-urchin-like catalyst, specifically a nickel-cobalt phosphide nanoneedle array on N-doped carbon nanospheres (Ni0.5Co1.5P@NCSs), for efficient HER by a sequential hydrothermal and low-temperature phosphating process. The catalyst exhibits sea-urchin-like structures, offering a specific surface area of 298 m2 g-1 and consequently furnishing a greater abundance of active sites. Comparing with non-sea-urchin-like Ni0.5Co1.5P@CN catalysts, the Ni0.5Co1.5P@NCSs exhibit an overpotential of 163 mV at 10 mA cm-2, a Tafel slope of 60 mV dec-1, and a maintained current density of approximately 90% during 50 h of continuous electrolysis. Experiments demonstrate that the outstanding electrochemical properties of the Ni0.5Co1.5P@NCSs originate from nitrogen doping of carbon spheres, the distinctive morphology of sea-urchin-like nanoneedle arrays, and simultaneous enhancements in intermediate adsorption energy, charge transfer, and electrolyte diffusion channel shortening. This work emphasizes a preparation strategy for synthesizing an attractive electrocatalyst with a low cost and efficient HER performance.

Interfacial π-p Electron Coupling Prompts Hydrogen Evolution Reaction Activity in Acidic Electrolyte.

The thermodynamically stable 2H-phase MoS2 is a brilliant material toward hydrogen evolution reaction (HER) owing to its excellent Gibbs free energy of hydrogen adsorption. Nevertheless, the poor intrinsic properties of 2H-MoS2 limit its electrocatalytic performances toward HER. In this work, graphitic carbon nitride covalently bridging 2H-MoS2 (MoS2/GCN) is proposed to construct robust HER electrocatalysts. The strong π-p electron coupling between the delocalized π electrons of GCN and the localized p electrons of S atoms sufficiently expose active sites and accelerate the reaction kinetics. To be specific, MoS2/GCN exhibits remarkable HER activity (160 mV at 10 mA·cm-2) and long-term durability. Importantly, MoS2/GCN also provides great potential for industrial application. Density functional theory (DFT) calculations disclose that the π-p electron coupling at the MoS2/GCN interface regulates the electronic structure of S atoms, consequently providing enhanced HER performance. This work presents a feasible pathway to develop advanced electrocatalysts for energy conversions.

Low content of Ni‐Pt nanoparticles decorated carbon nanofibers as efficient electrocatalyst for hydrogen evolution reaction

AbstractBackgroundAmong various technologies, electrochemical water splitting is one of the most effective and promising techniques for obtaining hydrogen fuel. The low content of nickel–platinum (Ni‐Pt) nanoparticles (NPs) decorated on carbon nanofibers (CNFs) have been developed by the electrospinning technique and subsequent carbonization process for use in an effective hydrogen evolution reaction (HER) in both acidic and alkaline mediums.ResultsThe Ni‐Pt ions are reduced to Ni‐Pt NPs during the carbonization process, while polyacrylonitrile nanofibers are simultaneously changed into carbon nanofibers. Field emission scanning electron microscopy (FE‐SEM) with energy dispersive X‐ray (EDX) and transmission electron microscopy (TEM) analysis of the prepared Ni‐Pt/CNFs shows that the low content of Ni and Pt NPs is evenly dispersed on the carbon nanofibers. This implies that for close contacts, there is an effective charge transfer between the NPs and the CNFs system. The obtained Ni‐Pt/CNFs exhibit enhanced HER performance along with onset potential (η1/23 mV in ~0 pH and η1/33 mV in ~14 pH) and overpotential (η10/128 mV in pH ~0 and η10/152 mV in pH ~14) versus RHE. Furthermore, stability for a long time was attained without considerable decay by 24 h. The turnover frequency (TOF) value was 3.431 s−1 in acidic and 1.174 s−1 in alkaline electrolytes.ConclusionThe enhanced HER performance could be ascribed to the synergetic effects between the carbon fibers and the Ni‐Pt NPs. This work demonstrates an easy technique for producing highly effective electrocatalysts for water splitting and has significant implications for renewable energy. © 2024 Society of Chemical Industry (SCI).

Crystalline/Amorphous‐Ru/VOx Phase Engineering Expedites The Alkaline Hydrogen Evolution Kinetics

AbstractActive and durable catalysts for hydrogen evolution reaction (HER) are of great significance for developing renewable hydrogen energy. Herein, crystalline/amorphous‐Ru/VOx (c/a‐Ru/VOx) heterogeneous catalysts are conceived, in which the amorphous VOx exposes more active sites and enhances charge transport compared with the counterpart with a crystal phase structure, strengthening the electronic interaction between metal‐support. As expected, c/a‐Ru/VOx‐500 with heat treatment at 500 °C exhibits excellent HER performance under alkaline conditions, with an overpotential of only 33 mV at 10 mA cm−2 and small Tafel slope (27 mV dec−1), superior to commercial platinum/carbon (Pt/C) catalysts. Particularly, its mass activity (0.335 A mgRu−1) is 1.5 times greater than that of Pt/C (0.224 A mgPt−1) at an overpotential of 50 mV. Also, it shows good industrial application prospects through tests under high temperature, high alkalinity, and large current conditions. Theoretical calculations unveil that there exists a charge redistribution at c/a‐Ru/VOx heterointerfaces, which makes the surface of Ru takes on an electron‐deficient state, resulting in optimization of adsorption and desorption for different reaction intermediates. This optimized behavior effectively reduces the thermodynamic energy barrier, allowing the catalyst with greatly enhanced HER performance. The exploration provides a promising strategy for designing efficient and durable catalysts for HER.

Enhanced Synergistic Effect by Facile Tuning of Nickel Doping on Cobalt Phosphide as Electrochemical Catalysts for Hydrogen Evolution Reaction in Alkaline Water Electrolysis

The development of efficient and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) is essential for alkaline water electrolysis. Cobalt phosphide (Co2P) is a promising non-noble electrocatalyst material for HER due to its low cost and high stability in alkaline solutions. However, improving the HER performance of Co2P is still challenging due to its catalytic mechanism in which Volmer reaction is the dominated rate-determining step. In this study, we introduced nickel to cobalt phosphide in order to improve its performance as an electrocatalyst because nickel is known to be beneficial for water dissociation (Volmer reaction), while cobalt is beneficial for producing gaseous hydrogen (Heyrovsky or Tafel reaction). This synergistic effect between nickel and cobalt phosphide contributes to enhancing HER performance. Also, it is crucial to find the optimal ratio of nickel and cobalt for maximizing synergistic effect. To facilitate the optimization process, a co-sputtering system was used to fabricate the electrodes. The resulting Ni-doped Co2P showed significantly enhanced HER performance with low overpotential of ~91 mV at 10 mA/cm2 and Tafel slope of ~47 mV/dec compared to pristine Co2P in electrochemical analysis. This enhancement is attributed from the optimized ratio between the sites where water dissociation and adsorbed hydrogen recombination reactions occur. The findings of this study demonstrate that the nickel cobalt phosphide electrode is a promising electrocatalyst for HER in alkaline water electrolysis.

Local pH Change during CoMo-TiO2 Composite Electrodeposition and Alkaline HER Electrolysis

Alloys of Co-Mo and Co-Mo-P are of interest for their ability to enhance the hydrogen evolution reaction (HER)1-2 and adding TiO2 to the alloy surface can further enhance HER.3-5 To better understand the influence of TiO2 particles on the electrodeposition of Co-Mo and Co-Mo-P alloys and the resulting HER kinetics, electrodeposition was conducted on a copper mesh electrode in close proximity to a pH probe to measure the local change of pH. The deposit composition and the HER characterized. There was a significant enhancement in the HER exchange current density when TiO2 particles were present in the alloy, taking into account any changes in the surface area. The enhancement was associated with a local pH change. Without TiO2 particles present in the solid state, the local pH change follows an expected increase with time as hydrogen is evolved and the hydroxide ion is generated at the electrode surface. In contrast, when TiO2 particles were present at the surface and in the metal alloy matrix, the local pH initially decreases slightly and remains constant (Fig 1). The results suggest that the enhanced HER performance with TiO2 in the alloy composite electrocatalyst is a consequence of the buffering of the local pH. In contrast, during electrodeposition there is little change in the pH transient with and without having TiO2 particles in the electrolyte. C. C. McCrory, A. Jung, I.M. Ferrer, S.M. Chatman, J.C. Peters, T.F. Jaramillo, J Am Chem Soc, 137 (13) 4347 (2015).A. C. Thenuwara, L. Dheer, N. H. Attanayake, Q. Yan, U. V. Waghmare, D. R. Strongin, ChemCatChem. 10 4832-4837 (2018).A.R. Shetty, A.C. Hegde, Mater. Sci. Energy Technol. 1 (2) 97 (2018).C. Wang, Hubert K. Bilan, E. J. Podlaha, J. Electrochem. Soc. 166 (10) F661 (2019).C. Wang and E. J. Podlaha, J. Electrochem. Soc. 167 (13) 132502 (2020). Figure 1. Change of pH during HER on a Co-Mo electrodeposit at different HER electrolysis current densities. Figure 1

Titanium Nanotubes as an Effective Electrocatalyst Support for Hydrogen Evolution Reaction

Developing proper support for hydrogen evolution reaction (HER) electrocatalysts is important for enhancing the HER efficiency and reducing the cost of green hydrogen production. TiO2-based-catalyst support has attracted considerable attention due to its commercial availability, high stability, low cost, and its unique electronic and ionic properties [1]. TiO2 is commonly utilized in various applications involving, photocatalysis, solar cells, and photoelectrochemical water splitting [2]. The ease of the synthesis of TiO2 with different morphologies and crystal structures makes it promising support to replace carbon in electrochemical applications [3]. Recently, anatase TiO2 nanoparticles decorated with PtOx clusters showed benchmark activity toward hydrogen evolution from the acidic medium with an overpotential of –125 mV at –10 mA cm–2 [4]. Furthermore, Pt clusters supported on porous TiO2 nanoparticles achieved higher stability compared with that of the benchmark Pt/C catalyst due to the facile electron transfer from TiO2 to PtOx [4]. Despite the TiO2-supported Pt nanoclusters have been recently investigated, the characteristic of HER electrocatalysts loaded on highly ordered TiO2 nanotube arrays (TNTs) is still unexplored. TNTs are expected to be an optimal support architecture owing to their large internal surface area and excellent electron mobility [5, 6]. Moreover, they can be readily synthesized and have robust mechanical stability. Therefore, in our work, highly ordered TNTs on Ti substrate have been synthesized and investigated as a support for different types of HER electrocatalysts (i.e. PtOx [7], MoS2 [8], and CoOP [9]). The PtOx clusters supported on TNTs (Ti/TNTs/PtOx) showed excellent performance for HER. An overpotential of –30 mV was sufficient to deliver –10 mA cm–2 from the acidic medium. The electrocatalytic mass activity of Ti/TNTs/PtOx (i.e. 204 mA mgPt –1) is enhanced by 12 and 1.7-fold compared to those of Pt/C and titanium nanoparticles (TNPs) supported PtOx electrocatalysts, respectively. The superior activity of the Ti/TNTs/PtOx is mainly due to its large electrochemically active surface area and the excellent electron mobility in the TNTs support. The immobilizing of MoS2 on TNTs resulted in enhanced electrocatalytic HER activity. An overpotential of –200 mVRHE was ample to deliver –10 mA cm–2 from 0.5 M H2SO4 aqueous solution. A synergy between the in-situ immobilized MoS2 and TNTs is proposed to explain the enhanced HER performance. In an alkaline medium, the Ti/TNTs/CoOP electrode fabricated by incorporating CoOP spheres into the TNTs exhibited only –130 mV overpotential to deliver –10 mA cm–2. This value is superior to that of CoOP deposited on bare Ti foil (–165 mV), FTO (–185 mV), and glassy carbon (–214 mV). In general, our study revealed that the TNTs support improves the electrochemical surface area and accessibility of active sites while reducing the charge transfer resistance at the electrode/electrolyte interface. Acknowledgments T.A.K. thanks the Deanship of Research Oversight and Coordination at KFUPM for the conference attendance support.

MOF-derived CoS2/WS2 electrocatalysts with sulfurized interface for high-efficiency hydrogen evolution reaction: Synthesis, characterization and DFT calculations

Developing high-efficiency, economical and non-noble-metal electrocatalysts is of great importance to produce hydrogen through hydrogen evolution reaction (HER) in water splitting. Transition metal dichalcogenide has received increasing interests in the application in efficient catalysis, energy conversion and storage. Now, a unique bimetallic sulfide composite (CoS2/WS2) has been prepared by calcination and one-pot hydrothermal method using metal–organic frameworks (MOFs) as precursors. The presence of suitable thioacetamide (TAA) plays a great role in forming the best sulfide interface between CoS2 and WS2 to enhance HER performance. Herein, the overpotential and Tafel slope of as-synthesized CoS2/WS2 at 10 mA cm−2 in 0.5 M H2SO4 medium are obtained as 79 mV and 52 mV dec–1, respectively, which are much lower than those of most non-noble metal-based electrocatalysts. Density Functional Theory (DFT) calculations verify that the bimetallic configuration through the sulfide interface changes the electronic structure, enhances the electrical conductivity and reduces the hydrogen adsorption energy (ΔGH*), effectively accelerating the Heyrovsky step in the HER process. Meanwhile, CoS2/WS2 shows excellent stability in durability tests. The method proposed in this work provides a feasible solution for synthesizing low-cost electrocatalysts.

Strategic design of NiS2/Co3S4 heterojunction for enhanced electrocatalytic hydrogen evolution in acidic media

The construction of heterogeneous interface significantly contributes to the boosted electrocatalytic activity for hydrogen evolution reaction (HER). This enhancement is achieved through the modulation of the electronic structure, facilitation of electron redistribution, and optimization of the electrocatalyst's chemisorption towards the reaction intermediates. Herein, NiS2/Co3S4 heterojunction was synthesized using a straightforward one-pot hydrothermal method, and the impact of heterogeneous interface on the electrocatalytic HER performances was investigated. The heterogeneous interface and strengthened interfacial effects between NiS2 and Co3S4 were confirmed by HRTEM and XPS. The NiS2/Co3S4 heterojunction demonstrate significantly enhanced HER performance in acidic solutions, owing to their clever structural design and the robust interfacial coupling effects within the heterogeneous interface structure, surpassing that of single-component NiS2 materials. The optimum NiS2/Co3S4 heterojunction presents a low overpotential of 253 mV and a Tafel slope of 62.0 mV dec−1 at 10 mA cm−2 toward HER. Density functional theory (DFT) calculation indicates that NiS2/Co3S4 heterostructure exhibit lower ΔGH* values compared to NiS2 and Co3S4. This suggests that the creation of heterogeneous interface can significantly optimize the adsorption capacity for hydrogen intermediates, thereby enhancing the HER in acidic media.

Tailoring the morphology of Mo2S3/MoP2 composite thin films via aerosol assisted chemical vapor deposition for enhanced hydrogen evolution reaction performance

In this study, we report on the fabrication of Mo2S3/MoP2 composite thin films using a single-step aerosol assisted chemical vapor deposition method from a single-source precursor solution of [(ƞ5-Cp)Mo(CO)2(S2P(SC6H4Me)2)] (1). Deposition times of 20, 30, and 40 min were used to obtain thin films with different morphologies. Our investigation found that the 30-minute thin film, which had a widely distributed grainy morphology, exhibited the highest electrocatalytic performance for hydrogen evolution reaction (HER) as determined by linear sweep voltammetry studies. This film required the lowest applied potential of 250 mV to generate a current density of 10 mAcm−2 with a low charge transport resistance of 715 Ω, despite having the lowest charge donor density of 5.52 × 1019 cm−3. We found that the unique morphology of this thin film enhanced electron mobility, resulting in superior HER performance with a Tafel slope of ∼123 mVdec−1 and a higher current charge density of 0.408 mAcm−2 due to increased active sites for HER. The Mo2S3/MoP2 heterostructure exhibited favourable band gaps of ∼2.2 and ∼2.7 eV, respectively, resulting in a synergistic effect that allowed for effective electron transfer. Our study concludes that different deposition durations produced composite thin films with altered morphologies that exhibit dissimilar electrochemical kinetics in HER.

Electrochemical activation of CoMo LDH nanosheets driving surface reconstruction for enhanced hydrogen evolution

Surface reconstruction emerging in the electrochemical oxygen evolution process is regarded to be significantly important for the activated catalysis efficiency, however, which is rarely recognized for hydrogen evolution reaction (HER). Here, the electrochemical activation of CoMo layered double hydroxide (CoMo-LDH) nanosheet arrays is demonstrated to significantly activate the electrochemical HER property. The catalysis performance improvement originates from the surface transformation of CoMo-LDH to Co(OH)2/CoOOH, as well as the dissolution of Mo and its adsorption on the catalyst surface in K2Mo3O10 phase. Based on the combined benefits of optimized electronic structure, increased catalysis sites, and promoted charge transfer, the overpotentials at catalysis current densities of 10 and 100 mA cm−2 are as low as 113 and 202 mV. This study demonstrates the electrochemical activation strategy to drive the surface reconstruction of bimetal hydroxides for enhanced HER performance, inspiring the research interests on the reconstruction and activation enhancement behaviors of HER electrocatalysts.

Tuning intrinsic defects of Pt-based carbon supports by high-energy ball-milling for enhanced alkaline hydrogen evolution

Carbon materials are significant supports for catalysts, in which surface properties play a crucial role in catalytic performances. However, the correlation between the intrinsic defects of carbon supports and the alkaline hydrogen evolution reaction (HER) performance of catalysts is still unclear. Herein, graphite (G) was used as a model support to study the effect of intrinsic defects of carbon support on the HER performance. To this end, defect-enriched graphite supports were obtained by a simple high-energy ball-milling process. The affluent intrinsic defects (edge surfaces) in graphite supports served as active sites for the dispersion and anchoring of Pt nanoparticles for better electron transfer from Pt species to the support, leading to strong metal-support interactions. The resulting Pt-loaded on defect-enriched DG-30 (Pt/DG-30) delivered a lower overpotential of 46 mV at 10 mA cm−2 when compared to undecorated Pt/G (177 mV), indicating an excellent HER activity. Pt/DG-30 also showed superior stability due to the strong metal-support interactions between Pt nanoparticles and carbon support. In sum, significant insights into the rational optimization and regulation of intrinsic defects of carbon supports were provided for the preparation of new catalysts-modified carbon supports with enhanced HER performances.

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.

Modulating metal-support interaction and inducing electron-rich environment of Ni2P NPs by B atoms incorporation for enhanced hydrogen evolution reaction performance

Modulation of the electronic interaction between the metal and support has been verified as a feasible strategy to improve the electrocatalytic performance of supported-type catalysts. Here, we have successfully synthesized an electrocatalyst of Ni2P nanoparticles (NPs) anchored on B, N co-doped graphite-like carbon nanosheets (Ni2P@B, N-GC), and elucidated the main mechanism by which B atoms doping enhances electrocatalytic hydrogen evolution reaction (HER) performance. The B atoms with electron-rich characteristic not only modulate the electronic structure on carbon skeleton, but also regulate the interfacial electronic interaction between Ni2P NPs and the carbon skeleton, which can lead to the increased available electron density of Ni sites. Such optimization is conducive to accelerating proton transfer and promoting reactive activity. As revealed, the Ni2P@B, N-GC catalyst with B atoms doping exhibits superior performance to the Ni2P@N-GC catalyst in acidic, neutral and alkaline medias. In addition, the assembled Ni(OH)2@B, N-GC||Ni2P@B, N-GC electrolyzer displays prominent overall water splitting performance in alkaline solution, which only demands 1.57 V to reach 10 mA/cm2, and in complicated natural seawater electrolyte, as low as 1.59 V. Hence, the B atoms doping strategy shows the significant enhancement for HER electrocatalysis.