Hydrogen Evolution Reaction Overpotential Research Articles

A Study on the Electrochemical Performance of MOF Based HER Catalysts for Anion Exchange Membrane Water Electrolysis

Recently, research on anion exchange membrane water electrolysis (AEMWE) has been conducted, which has the advantage of using a non-noble transition metal catalyst to reduce cost and improve the activity and durability of the catalyst. In alkaline solutions, heterojunction catalysts are favored because the rational design of catalysts requires the ability to simultaneously dissociate water and bind hydrogen species.In this study, N-doped carbon hollow polyhedron (NCHP) supports were synthesized using two types of metal-organic frameworks (MOFs) to enhance catalyst durability by effective active site-support interactions. Moreover, well dispersed MoC on MOFs with regularly connected metal nodes and organic ligands increased the number of active sites and improved the reaction kinetics owing to the synergistic effects between MoC and Co@NC, which enhanced the hydrogen evolution reaction (HER).The formation mechanism of NCHP was confirmed by transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. During the half-cell test, the incorporation of MoC (MoC-Co@NC/NCHP) reduced the HER overpotential by approximately 1.8 times at 10mA/cm2 compared with that of Co@NC/NCHP. Furthermore, durability cycling was conducted from 0.1 to -0.6 V versus a reversible hydrogen electrode (RHE). The durability tests revealed that after 3000 cycles, the reduction in the HER current of MoC-Co@NC/NCHP was 1.4 and 2.7 times lower than those of Co@NC/NCHP and commercial Pt/C, respectively. This study provides two strategies to obtain highly stable NC matrix supports and highly active heterojunction catalysts.

Highly porous interconnected MoP decorated graphene oxide as remarkably efficient electrocatalyst

Hydrogen (H2) production through water splitting has less viable applications due to the unfavourable kinetics of the reaction. Electrocatalysts with a robust structure, high levels of catalytic activity, and a high degree of stability are in high demand but challenging. This paper reports the synthesis of highly porous interconnected molybdenum phosphide (MoP) assembled with graphene oxide (GO) to form MoP/RGO hybrid electrocatalysts in a novel phosphorization process at a reasonably low temperature under an argon (Ar) atmosphere by a mixing and heat-treating method for the hydrogen evolution reaction (HER). Bifunctional MoP anchored on reduced graphene oxide (MoP/RGO) porous structures exhibited extra permeability for ion and electrolyte transport. An efficient MoP/RGO-based electrocatalyst exhibited brilliant electrocatalytic performance, having HER overpotential of 96 mV at a current density of 10 mA/cm2 with a low Tafel slope of 64 mV/dec in an alkaline solution. The effectiveness of an optimised electrocatalyst indicates significant HER activity for all intermediate chemical reactions. A highly efficient electrocatalyst also exhibited long-term stability with a minor potential decrease over 24 h. RGO shows great potential as a material possessing remarkable strength in the context of high temperature phosphorization. It effectively hinders particle agglomeration, enhances catalyst conductivity, and ultimately betters both the performance and durability of an electrocatalyst in HER applications.

Confined synthesis of highly dispersed Ni anchored on mesoporous carbon as efficient catalyst for water splitting

Developing an efficient and low-cost bifunctional electrocatalysts with superior activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is highly required but still challenging. Herein, highly dispersed Ni species containing both Ni nanoparticles (NPs) and atomically dispersed Ni-NX on mesoporous nitrogen-doped carbon (Ni-N-C) were prepared by a facile one-pot pyrolysis strategy using dicyandiamide, citric acid and nickel acetylacetonate as raw materials. The confinement agent citric acid is quite requisite for dispersing Ni NPs and forming mesoporous graphene-like carbon substrate. Due to the uniform size of Ni NPs (3 nm) and the synergistic effect between Ni NPs and Ni-NX, and the unique mesoporous carbon structure, such Ni-N-C catalyst exhibits favorable activities for both HER and OER. The overpotentials for HER and OER are only 218 and 330 mV vs. RHE on glassy carbon to deliver a current density of 10 mA·cm−2, respectively. Moreover, this catalyst also showed good operation durability with no obvious deactivation after long-term (18 h) potentiostatic electrolysis or continuous CV tests. This work could offer a new avenue for the design of bifunctional electrocatalysts in efficient water splitting.

Double‐Tuned RuCo Dual Metal Single Atoms and Nanoalloy with Synchronously Expedited Volmer/Tafel Kinetics for Effective and Ultrastable Ampere‐Level Current Density Hydrogen Production

AbstractAlkaline water electrolysis system is of general interest but is impeded by the unsatisfactory hydrogen evolution reaction (HER) performance under ampere‐level current density. Herein, the synchronous modification of complicated Volmer/Tafel kinetics is effectuated for attaining ampere‐level current density hydrogen production via engineering double‐tuned RuCo nanoalloy and dual metal single atoms on hierarchical N‐doped mesoporous carbon (RuCo@RuSACoSA‐NMC). The electronic structure of Ru sites in dual metal single atoms can be synergistically tailored by adjacent Co atomic sites and nanoalloy, which makes it achieve faster Volmer kinetics with rapid water adsorption/dissociation and transfer rates toward adsorbed hydroxyl. While double‐tuned Ru sites in nanoalloy by adjacent alloyed Co sites and dual metal single atoms undertake optimized Tafel kinetics with boosted transfer rates toward adsorbed hydrogen. Accordingly, RuCo@RuSACoSA‐NMC exhibits ultralow HER overpotential of 255 mV at 1 A cm−2 with robust stability over 24 days, ultrahigh mass activity of 37.2 A mgRu−1, and turnover frequency of 19.5 s−1. More importantly, RuCo@RuSACoSA‐NMC can make water electrolysis system possess low power consumption of 5.34 kWh per Nm3H2 and estimated costs of 1.197 $ per kgH2. The concept emphasized in this study provides guidance for rational design of cost‐effective catalysts with ampere‐level current density hydrogen production.

A novel electrochemical sensor based on HER overpotential of Ag-Cu bimetallic catalyst

Conventional electrochemical (EC) sensors usually rely on modifying redox substances to generate signal, which may lead to the requirement of complex modification processes and abnormal signal fluctuation. In addition, many redox substances would cause potential risks to the environment. To solve these issues, a novel environmentally friendly electrochemical sensor based on hydrogen evolution reaction (HER) was established, and the overpotential of Ag-Cu bimetallic HER catalyst was used as signal to avoid using redox substances. As a proof of concept, a model tumor marker, matrix metalloproteinase-3, was detected by this sensor with a wide linearity ranging from 0.001 to 100 ng mL−1 and a low limit of detection of 2.02 fg mL−1. These results illustrated great sensing performances. This method provided a new direction in designing novel eco-friendly EC sensors and application of HER catalysts.

Iron doping and interface engineering on amorphous/crystalline Fe-NixSy heterostructures toward high-stability and kinetically accelerated water splitting

It is very important to develop transition metal-based electrocatalysts with excellent activity, high stability and low-cost for overall water splitting. In this work, the Fe-doped NixSy/NF amorphous/crystalline heterostructure nanoarrays (Fe-NixSy/NF) was synthesized by a simple one-step method. The resulting hierarchically structured nanoarrays offer the advantages of large surface area, high structural void fraction and accessible internal surfaces. These advantages not only furnish additional catalytically active sites, but also enhance the stability of the structure and effectively accelerate mass diffusion and charge transport. Experimental and characterization results indicate that Fe doping increases the electrical conductivity of amorphous/crystalline NixSy/NF, and the NiS-Ni3S2 heterojunctions evoke interfacial charge rearrangement and optimize the adsorption free energy of the intermediates, which allows the catalyst to exhibit low overpotential and superior electrocatalytic activity. Especially, the overpotentials of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of Fe-NixSy/NF at 10 mA cm−2 in an alkaline environment are 102.4 and 230.5 mV, respectively. When applied as a bifunctional catalyst for overall water splitting, it requires only 1.45 V cell voltage to deliver a current density of 10 mA cm−2, which is preferable to the all-noble metal Pt/C || IrO2 electrocatalyst (1.62 mV @ 10 mA cm−2). In addition, Fe-NixSy/NF has excellent stability, and there is no obvious degradation after 96 h continuous operation at a current density of 100 mA cm−2. This work affords insights into the application of doping strategies and crystalline/amorphous synergistic modulation of the electrocatalytic activity of transition metal-based catalysts in energy conversion systems.

A Low‐Cost, Durable Bifunctional Electrocatalyst Containing Atomic Co and Pt Species for Flow Alkali‐Al/Acid Hybrid Fuel Cell and Zn–Air Battery

AbstractTransition metal single atoms anchored on nitrogen‐doped carbon (M‐N‐C) matrix with M‐N‐C active sites have shown to be promising catalysts for both hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Herein, a hybrid catalyst with low‐level loading of atomic Pt and Co species encapsulated in nitrogen‐doped graphene (Pt@CoN4‐G) is developed. The Pt@CoN4‐G shows low overpotential for HER in wide‐pH electrolyte and manifests improved mass activity with almost eight times greater than that of Pt/C at an overpotential of 50 mV. The Pt@CoN4‐G also exhibits a top‐level ORR activity (half‐wave potential, E1/2 = 0.893 V) and robust stability (>200 h) in alkaline medium. Using theoretical calculations and comprehensive characterizations , the strong metal–support interactions between Pt species and CoN4‐G support and synergistical cooperation of multiple active sites are clarified. A flow alkali‐Al/acid hybrid fuel cell using Pt@CoN4‐G as cathode catalyst delivers a large power density of 222 mW cm−2 with excellent stability to achieve simultaneously hydrogen evolution and electricity generation. In addition, Pt@CoN4‐G endows a flow Zn‐air battery with high power density (316 mW cm−2), good stability under large current density (>100 h at 100 mA cm−2), and long cycle life (over 600 h at 5 mA cm−2).

Ni-CeO2 Heterostructure Promotes Hydrogen Evolution Reaction via Tuning of the O-H Bond Length of Adsorbed Water at the Electrolyte/Electrode Interface.

Understanding the properties and structure of reactant water molecules at the electrolyte solution/electrode interface is relevant to know the mechanisms of hydrogen evolution reaction (HER). However, this approach has rarely been implemented due to the elusive local microenvironment in the vicinity of the catalyst. Taking the Ni-CeO2 heterostructure immobilized onto carbon paper (Ni-CeO2 /CP) as a model, the dynamic behavior of adsorbed intermediates during the reaction was measured by in situ surface-enhanced infrared absorption spectroscopy with attenuated total reflection configuration (ATR-SEIRAS). Theoretical calculations are used in combination to comprehend the potential causes of increased HER activity. The results show that the O-H bond of adsorbed water at the electrolyte solution/electrode interface becomes longer for promoting the dissociation of water and accelerating the kinetically slow Volmer step. In addition, forming the Ni-CeO2 heterostructure interface optimizes the hydrogen adsorption Gibbs free energy, thus increasing HER activity. Therefore, the Ni-CeO2 /CP electrode exhibits remarkably low HER overpotentials of 37 and 119 mV at 10 and 100 mA cm-2 , which are close to commercial Pt/C (16 and 102.6 mV, respectively).

Modulation of the electronic structure of Co2P by Mo, Fe co-doping for efficient urea electrolysis

Hydrogen production by urea splitting not only plays an energy-saving role in the production of hydrogen energy, but also can purify wastewater containing urea, which has great advantages compared with hydrogen production by water splitting. In this study, Mo, Fe co-doped bifunctional Co2P electrodes were prepared through hydrothermal and moderate-temperature phosphating methods. Under the synergistic effect of bimetallic cations, the electronic structure of Co2P is effectively modulated, thus showing excellent electrochemistry performance in urea splitting. In the electrolyte solution of 1 M KOH and 0.5 M urea, the potential of urea oxidation reaction (UOR) is 1.26V, 1.316 V and 1.336V for driving current density of 10, 50 and 100 mA cm−2, and the overpotential of hydrogen evolution reaction (HER) is 194 mV, 244 mV and 268 mV for driving current density of 10, 50 and 100 mA cm−2. The overall urea electrolysis only requires a voltage of 1.415 V and 1.686 V to drive a current density of 10 and 50 mA cm−2, which is one of the best catalytic activities reported to date. The experimental results show that the increased activity is assigned to the rapid charge transfer, the exposure of more active sites and the improved conductivity due to the doping of bimetallic ions. Density functional theory (DFT) demonstrates that the prepared Mo, Fe co-doped Co2P electrodes has the smallest Gibbs free energy for hydrogen adsorption compared with Fe co-doped Co2P electrodes. This work laid a new foundation for the synthesis of bimetallic cation-doped transition metal phosphide (TMP) for urea-assisted water splitting.

Alloyed Ru0.48Re0.52 nanocatalysts with electronic structure regulation for intensified alkaline hydrogen evolution reaction

Converting electricity into hydrogen is vital for harnessing concentrated renewable energy. To achieve this, cost-effective electrocatalysts capable of withstanding mildly corrosive alkaline hydrogen evolution reaction (HER) conditions are necessary. Ru shows potential as a substitute for Pt-based electrocatalysts due to its comparable hydrogen bond strength. However, improvements are needed to overcome obstacles in water dissociation and hydrogen desorption during alkaline HER. In this work, Ru was alloyed with Re which is water dissociation-efficient to induce a redistribution of electron density in Ru0.48Re0.52 nanoparticles (NPs). These Ru0.48Re0.52NPs exhibited superior hydrogen desorption, outperforming Pt, highlighting their effectiveness in HER. The Re component received electrons from adjacent Ru while maintaining low energy barriers for water decomposition. Additionally, self-aggregation of Ru0.48Re0.52NPs was prevented by incorporating reduced graphene oxide (rGO) support, resulting in improved conductivity and electrochemical durability in Ru0.48Re0.52NPs@rGO. Through various analyses, the optimal synthesis and electronic structure adjustments in Ru0.48Re0.52NPs@rGO were confirmed, which exhibited remarkable HER overpotentials with values of 14 and 74 mV at current densities of 10 and 100 mA cm−2, respectively, in a 1 M KOH solution. These findings establish Ru0.48Re0.52NPs@rGO as a universal approach for designing efficient electrocatalysts for HER, surpassing both the activity and cost of commercialized Pt/C.

Cactus-like amorphous MoS2-CoFeLDO heterostructures for alkaline hydrogen evolution reaction

Designing efficient and stable non-precious metal catalysts with heterogeneous structures for electrolytic hydrogen evolution in alkaline media is a challenging topic. Cactus-like amorphous MoS2-CoFeLDO heterostructures derived from calcination of MoS2-CoFeLDH in argon markedly reduced overpotential of hydrogen evolution reaction (HER). The HER overpotential of MoS2-CoFeLDO@400 °C in 1 M KOH solution required only 36 mV to reach a current density of 10 mA/cm2 and remained highly active for ≥24 h. Finite element simulations showed that cactus-like tip generated higher charge intensity, then aggregated electrons induced a higher electric field for local H+ enrichment. XRD and TEM analyses confirmed amorphous MoS2 with abundant hydrogen evolution sites in MoS2-CoFeLDO@400 °C. DFT calculations demonstrated that MoS2-CoO had a 0.5 eV lower reaction energy barrier than MoS2-CoFeLDH in the Tafel step, indicating superior reaction kinetics to promote HER.

A Strongly Coupled Ag(S)@NiO/Nickel Foam Electrode Induced by Laser Direct Writing for Hydrogen Evolution at Ultrahigh Current Densities with Long-Term Durability.

Highly active, durable, and cost-effective electrodes for hydrogen evolution reaction (HER) at ultrahigh current densities (≥1 A cm-2 ) are extremely demanded for industrial high-rate hydrogen production, but challenging. Here, a robust strongly coupled Ag(S)@NiO/nickel foam (NF) electrode is reported. Taking advantage of millisecond laser direct writing in liquid nitrogen technique, lattice-matched and coherent interfaces are formed between Ag nanoparticles with stacking faults (denoted by Ag(S)) and NiO nanosheets, leading to strong interfacial electronic coupling, not only promoting H2 O adsorption and dissociation on Ni2+ but also enhancing H* adsorption on intrinsically inactive but most electrically conductive Ag. Strong chemical bonding is established at NiO/NF interface, guaranteeing rapid electron transfer and excellent mechanical durability under high-rate hydrogen evolution. The physicochemically stable electrode achieves record-low alkaline HER overpotential of 167 and 180mV at 1 and 1.5 A cm-2 , respectively, along with negligible activity decay after 120h test at ≈1.5 A cm-2 , surpassing reported non-platinum group metal electrocatalysts.

Activation of Osmium by the Surface Effects of Hydrogenated TiO2 Nanotube Arrays for Enhanced Hydrogen Evolution Reaction Performance.

Efficient cathodes for the hydrogen evolution reaction (HER) in acidic water electrolysis rely on the use of expensive platinum group metals (PGMs). However, to achieve economically viable operation, both the content of PGMs must be reduced and their intrinsically strong H adsorption mitigated. Herein, we show that the surface effects of hydrogenated TiO2 nanotube (TNT) arrays can make osmium, a so far less-explored PGM, a highly active HER electrocatalyst. These defect-rich TiO2 nanostructures provide an interactive scaffold for the galvanic deposition of Os particles with modulated adsorption properties. Through systematic investigations, we identify the synthesis conditions (OsCl3 concentration/temperature/reaction time) that yield a progressive improvement in Os deposition rate and mass loading, thereby decreasing the HER overpotential. At the same time, the Os particles deposited by this procedure remain mainly sub-nanometric and entirely cover the inner tube walls. An optimally balanced Os@TNT composite prepared at 3 mM/55 °C/30 min exhibits a record low overpotential (η) of 61 mV at a current density of 100 mA cm-2, a high mass activity of 20.8 A mgOs-1 at 80 mV, and a stable performance in an acidic medium. Density functional theory calculations indicate the existence of strong interactions between the hydrogenated TiO2 surface and small Os clusters, which may weaken the Os-H* binding strength and thus boost the intrinsic HER activity of Os centers. The results presented in this study offer new directions for the fabrication of cost-effective PGM-based catalysts and a better understanding of the synergistic electronic interactions at the PGM|TiO2 interface.

Defective Amorphous Carbon‐Coated Carbon Nanotube‐Loaded Ruthenium Nanoparticles as Efficient Electrocatalysts for Hydrogen Production

Compared with hydrogen evolution reaction (HER) under acidic conditions, the kinetic steps of alkaline HER are more complex, which involves the adsorption and cleavage of water molecules. Defect and interface engineering are two important means to enhance basic HER. In order to prepare catalysts with high activity and stability under both acidic and basic conditions, a defective amorphous carbon loaded with Ru nanoparticles coaxially wrapped around a carbon nanotube (CNT) sponge network is presented. The presence of amorphous carbon can promote the uniform loading of Ru nanoparticles and limit the growth of Ru nanoparticles, and also the introduction of oxygen defects can regulate the electronic structure of the metal and improve its charge transport capacity, thus enhancing the catalytic performance. The catalyst CNT/C/Ru0.37 wt%‐700 prepared under optimized conditions exhibits excellent stability and activity. At a current density of 10 mA cm−2, the overpotential of HER is as low as 38.3 and 36.2 mV under alkaline and acidic conditions, respectively, which is better than most reported Ru‐based catalysts. This study details innovative and feasible ideas for the design and preparation of loaded catalysts, which can contribute to the development of high‐performance electrochemical catalysts.

IrCo single-atom alloy catalysts with optimized d-band center for advanced alkali-Al/acid hybrid fuel cell

Electrochemical energy storage/conversion by utilizing hydrogen (H2) an energy carrier is promising for alleviating the energy crisis. As an emerging H2 production technique, alkali/acid hybrid fuel cell has been reported to exhale H2 and generate electric power spontaneously, which requires highly effective and economically feasible electrocatalysts for cathodic hydrogen evolution reaction (HER). Herein, IrCo single atom alloy catalysts (SAACs) encapsulated in nitrogen-doped carbon nanotubes (IrCo@NCNTs) was prepared as cathode catalyst for alkali-Al/acid hybrid fuel cell (3AHFC). IrCo@NCNTs with low Ir loading of 2.17 wt% exhibits very low overpotentials for HER in pH-wide electrolytes (pH = 0 and 14) and achieves improved mass activity, which are 8 times and 13 times greater than that of Pt/C in acidic and alkaline medium, respectively. Density functional theory (DFT) calculations reveal that the high HER activity derives from the lowing of d-band center by introducing Ir, which is favors to tune the electronic structures, leading to the optimized H⁎ adsorption. The assembled IrCo@NCNTs 3AHFC offers a high power density 176.2 mW cm−2, a high hydrogen production rate of 453.0 L m-2 h−1 with high Faradic efficiency of 99.1%, which can compete with those in commercial 20 wt% Pt/C and most reported platinum-free catalysts.

A high-performance self-supported multifunctional NF@Pt electrocatalyst for overall water splitting and rechargeable zinc-air battery

Developing multifunctional electrocatalysts has been a lasting challenge. Herein, with dual surface guiding agents NaI and PVP, uniformly dispersive Pt nanoclusters on self-supported nickel foam (NF@Pt-1) has been fabricated with low Pt loading. The obtained NF@Pt-1 performs excellently in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), overall water splitting and rechargeable zinc-air battery. The NF@Pt-1 exhibits low HER overpotentials of 32.8 mV in alkaline solution and 50 mV in acidic solution at 10 mA cm−2. At a high current density of 100 mA cm−2, the overpotential for HER in alkaline solution is only 72.3 mV. The OER overpotential of NF@Pt-1 is 307 mV at 20 mA cm−2. All of these drive a 1.575 V overall water splitting potential. In rechargeable zinc-air battery, the recharging polarization voltage is only 0.869 V, 0.107 V smaller than that of the battery constructed with Pt/C. The excellent performances and the wide range of applications would be ascribed to the highly dispersion of Pt nanoclusters on self-support nickel foam under proper guiding effect of dual surface guiding agents. This work has explored an effective route for fabricating multifunctional electrocatalysts with relatively high performance-cost ratio.

Modulating Electronic Structure of PtCo-Ptrich Nanowires with Ru atoms for Boosted Hydrogen Evolution Catalysis.

Rational design and development of highly efficient hydrogen evolution reaction (HER) electrocatalysts is of great significance for the development of green water electrolysis hydrogen production technology. Ru-engineered 1D PtCo-Ptrich nanowires (Ru-Ptrich Co NWs) are fabricated by a facile electrodeposition method. The rich Pt surface on 1D Pt3 Co contributes to the fully exposed active sites and enhanced intrinsic catalytic activity (co-engineered by Ru and Co atoms) for HER. The incorporation of Ru atoms can not only accelerate the water dissociation in alkaline condition to provide sufficient H* but also modulate the electronic structure of Pt to achieve optimized H* adsorption energy. As a result, Ru-Ptrich Co NWs have exhibited ultralow HER overpotentials (η) of 8 and 112mV to achieve current densities of 10 and 100mA cm-2 in 1m KOH, respectively, which far exceed those of commercial Pt/C catalyst (η10 =29mV, η100 =206mV). Density functional theory (DFT) calculations further demonstrate that the incorporated Ru atoms possess strong water adsorption capacity (-0.52 vs -0.12eV for Pt), facilitating water dissociation. The Pt atoms in the outermost Pt-rich skin of Ru-Ptrich Co NWs achieve optimized H* adsorption free energy (ΔGH* ) of -0.08eV, boosting hydrogen generation.

Unveiling the Effect of Organic Sulfur Sources on Synthesized MoS2 Phases and Electrocatalytic Hydrogen Evolution Performances

Metallic-phase MoS2 exhibits Pt-comparable electrocatalytic hydrogen evolution reaction (HER) performance in acidic conditions. However, the controllable synthesis of metallic-phase MoS2 is quite challenging because the key factor determining the phase types of MoS2 during synthesis is still unclear. Herein, the effect of organic sulfur sources on the formed MoS2 phase is studied by use of thioacetamide (TAA), l-cysteine, and thiourea as sulfur sources. The TAA and l-cysteine produce metallic MoS2, while thiourea gives rise to semiconducting MoS2. Owing to the metallic phase and smaller size, the MoS2 prepared with TAA and l-cysteine has a higher electrocatalytic HER activity than the MoS2 obtained from thiourea. The HER overpotential of MoS2 synthesized with TAA is only 210 mV for reaching the current density of 10 mA/cm2, and the corresponding Tafel slope is 44 mV/decade. Further studies find that the decomposition temperature of sulfur precursors is the key factor for the formation of metallic MoS2. Sulfur precursors with a lower decomposition temperature release sulfur ions quickly, which in turn stabilize the metallic phase and inhibit the growth of MoS2 into large sizes. Our findings unveil the key factor for controlling the phase type of MoS2 synthesized from organic sulfur precursors and will be very helpful for the synthesis of MoS2 with high electrocatalytic activity.

Interfacial Engineering of NiFeP/NiFe-LDH Heterojunction for Efficient Overall Water Splitting

In consideration of application prospect of non-noble metallic materials catalysts, the study of exploring more highly effective electrocatalysts has been focused on by researchers. Herein, a novel strategy is employed to construct a heterojunction consisting of metal phosphide NixFeyP and layered double hydroxide (LDH) with graphene oxide (GO) as conductive support. By adjusting the molar ratio of Ni to Fe, a series of heterojunctions with mixed valence state Feδ+/Fe3+ and Niδ+/Ni2+ (δ is likely close to 0) redox couples are achieved and strong synergistic effects towards overall water splitting performance are found. The optimized catalyst with a Ni/Fe molar ratio of 0.72:0.33, namely Ni0.7Fe0.3P/LDH/GO, delivers ultra-low overpotentials for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of 79 and 198 mV at the current density of 10 mA•cm-2, respectively. Furthermore, for overall water-splitting practical application, it only requires 1.526 V at 10 mA•cm-2 with robust stability, which is superior to most reported electrocatalysts. Experimental results demonstrate the improved electronic conductivity, enlarged electrochemically active area and accelerated kinetics together account for the enhanced performance. This work supplies new prospects for the promotion and application of such heterojunction electrocatalysts in overall water splitting.

Efficient and stable electrocatalytic performances of nanostructured composite of CuO and Co2P in the full pH range towards hydrogen and oxygen evolution

It is highly desirable to explore non-noble metal catalysts with outstanding intrinsic activity and abundant active sites to ensure efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in the full pH range. In this article, we have prepared a nanoflower-shaped composite material of CuO and Co2P (CuO@Co2P) by extending nanowires on foam copper, which effectively increased the contact area while ensuring stability and conductivity. The synergistic effect between CuO and Co2P promotes the reactivity of HER and OER in the full pH range. For example, the CuO@Co2P/NF electrode requires only the overpotentials of 150 and 374 mV for HER to achieve 10 and 100 mA·cm−2 respectively, and 260 and 391 mV for OER current densities of 10 and 100 mA·cm−2, in 1 M KOH medium. And in a neutral electrolyte of 0.5 M Na2SO4, achieve the same current density values as 10 and 100 mA·cm−2, requires the overpotentials of 82 and 213 mV for HER, and 301 and 472 mV for OER, respectively. Furthermore, the HER overpotential of 206.3 mV is needed up to 100 mA·cm−2 in 0.5 M H2SO4 medium for CuO@Co2P/NF electrode. The composite CuO@Co2P has an excellent electrochemical stability, which shows only 7.12%, 4.02% and 5.3% of current density attenuation during HER tested in 0.5 M H2SO4, 0.5 M Na2SO4 and 1 M KOH, respectively, and the rates of change in the OER process in 0.5 M Na2SO4 and 1 M KOH media are 4.79% and 3.46%. This work expands the efficient application of electrocatalysts in the full pH range and avoids the release of toxic gases during phosphating, which is of great significance for the development of transition metal phosphating composite electrocatalysts.