Electrode For Overall Water Splitting Research Articles

Porous TiN-based ceramic electrode with N-modified Co-based Nanorods/TiN heterointerfaces for efficient overall water splitting

The development of high-performance electrocatalytic electrodes for overall water splitting is a crucial issue to realize renewable hydrogen production. This paper presents the in situ growth of N-modified Co-based nanorods on porous TiN ceramic membranes using the hydrothermal method and thermal NH3 treatment, resulting in a novel self-supported electrocatalytic electrode with abundant heterointerfaces, denoted as NCTN-x-y (x: nitridation temperature; y: nitridation time). In the alkaline medium (1 M KOH), the NCTN-350-2 electrode displays the best hydrogen evolution reaction (HER) activity (ƞ10 = 66 mV), and the NCTN-250-3 electrode manifests the best oxygen evolution reaction (OER) performance (ƞ10 = 270 mV). Accordingly, these two electrodes comprise an electrolyzer, which features a current density of 10 mA cm−2 at a low cell voltage of 1.63 V. The good electrocatalytic performance can be attributed to the abundant heterointerfaces formed between the porous TiN ceramic membrane and the N-modified Co-based nanorods, in conjunction with the hierarchical pore structure of the TiN ceramic membrane. Theoretical calculations identify that the construction of heterointerfaces modulates the electronic structure of active sites, thereby promoting the dissociation of H2O, optimizing the H* adsorption energy (ΔGH*), and accelerating the reaction kinetics, which ultimately improve the electrocatalytic activity of electrode.

Heterogeneous strategy constructing a built-in electric field: CoP/FeP bifunctional electrode for overall water splitting

Development of non-noble bifunctional electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are of great significance under alkaline electrolytes for overall water splitting. In this work, CoP/FeP has been designed and constructed in situ on carbon fiber paper by using the bimetallic metal organic frameworks (MOFs) synthesis strategy. The heterogeneous CoP/FeP displays excellent catalytic activities in both HER and OER of the fully hydrolyzed semi-reaction. Remarkably, CoP/FeP is applied as the bifunctional electrode in anode and cathode to construct an overall water splitting apparatus, resulting in the low cell voltage and excellent stability. The exceptional electrocatalytic performance may be mainly attributed to the heterogeneous interface, which constructs a built-in electric field to provide electron to Co with electron-rich structure, resulting in the strong adsorption of H and weak adsorption of O2 on Co. This study provides an effective and controllable method for the design of self-supporting bimetal phosphide catalysts.

Electrocatalytic overall water splitting based on (ZnNiCoFeY)xOy high-entropy oxide supported on MoS2

Hydrogen energy is a sustainable and clean source that can meet global energy demands without adverse environmental impacts. High-entropy oxides (HEOs), multielement (5 or more) oxides with an equiatomic or near-equatomic elemental composition, offer a novel approach to designing bifunctional electrocatalysts. This work explores (ZnNiCoFeY)xOy over MoS2 as a bifunctional electrocatalyst (HEO–MoS2) in an alkaline medium. The HEO was synthesized using a combustion process and loaded over MoS2 using an ultrasonic method. The synthesized HEO over MoS2 exhibits excellent performance, including long-term stability for over 24 h, an overpotential of 214 mV vs the reversible hydrogen electrode (RHE) for the hydrogen evolution reaction (HER), and 308 mV for the oxygen evolution reaction (OER) at 10 mA cm−2. This bifunctional electrocatalyst exhibits low overpotential for both the HER and the OER at high current densities. Additionally, HEO–MoS2 demonstrates smaller solution and charge transfer resistance values. The electrolyzer was assembled using bifunctional HEO–MoS2 electrodes for overall water splitting. These electrodes exhibited a low cell voltage of 1.65 V at 10 mA cm−2. The novel electrocatalyst was fabricated using a facile and scalable method that appeals to industrial applications.

Rational design of bimetallic metal-organic framework derived three-dimensional flower-like and porous NiCoFe LDH/NF electrocatalyst for electrochemical overall water splitting

Porous structured metal–organic frameworks (MOFs) and their derivatives are desired in catalysis and energy storage. Herein, three-dimensional (3D) flower-like NiCoFe LDH/NF are first synthesized though a convenient cathodic electrodeposition strategy subsequent an ion-exchange process. And the morphology and catalytic performance of the CoFe-MOF/NF can be finely by tailoring the electrodeposition voltage, deposition time and the ratio of Co: Fe. The 3D flower-like and porous NiCoFe/NF not only retains structural integrity to promote durability but also greatly alleviates the aggregation of active sites. In addition, the 3D flower-like and porous NiCoFe/NF display remarkable results with low overpotentials of 233 mV at a current density of 50 mA cm−2 for OER and 84 mV at a current density of 10 mA cm−2 for HER in 1 M KOH, respectively. When acting as electrocatalytic electrodes for overall water splitting, NiCoFe/NF displays a low overpotential of 1.52 V to achieve a current density of 10 mA cm−2. The study provides a promising approach to design MOF electrocatalysts for electrocatalytic applications.

Electronic Modulation in Cu Doped NiCo LDH/NiCo Heterostructure for Highly Efficient Overall Water Splitting

AbstractLayered double hydroxides (LDHs), promising bifunctional electrocatalysts for overall water splitting, are hindered by their poor conductivity and sluggish electrochemical reaction kinetics. Herein, a hierarchical Cu‐doped NiCo LDH/NiCo alloy heterostructure with rich oxygen vacancies by electronic modulation is tactfully designed. It extraordinarily effectively drives both the oxygen evolution reaction (151 mV@10 mA cm−2) and the hydrogen evolution reaction (73 mV@10 mA cm−2) in an alkaline medium. As bifunctional electrodes for overall water splitting, a low cell voltage of 1.51 V at 10 mA cm−2 and remarkable long‐term stability for 100 h are achieved. The experimental and theoretical results reveal that Cu doping and NiCo alloy recombination can improve the conductivity and reaction kinetics of NiCo LDH with surface charge redistribution and reduced Gibbs free energy barriers. This work provides a new inspiration for further design and construction of nonprecious metal‐based bifunctional electrocatalysts based on electronic structure modulation strategies.

Stable overall water electrolysis performance of interface engineered Y2Ru2O7/NiMoO4@NF in alkaline solution

Problems faced in water electrolysis, such as sluggish reaction kinetics and poor electrode stability, can be overcome by developing electrode materials with tailormade properties. Introducing a nanostructured interface with pyrochlore materials is an efficient but complex strategy. This study focused on the interface engineering of the pyrochlore Y2Ru2O7/NiMoO4@NF. The material was found to show significantly high overall water splitting performance in 1 M KOH electrolyte solution. Specifically, the prepared Y2Ru2O7/NiMoO4@NF showed oxygen evolution and hydrogen evolution overpotentials of 287 and 112 mV at a current density of 10 mA cm−2, respectively. A Y2Ru2O7/NiMoO4@NF electrode with higher stability that was prepared rationally required a cell voltage of only 1.613 V to achieve a current density of 10 mA cm−2 for alkaline water electrolysis. This showed the excellent catalytic ability of the electrode for overall water splitting. In particular, the temperature dependence of the electrode’s performance in water electrolysis in a practical water electrolyzer was examined to ascertain the electrode’s suitability for use on an industrial scale; the operating temperature of the electrolyzer was varied in the range 25–75 °C. The observed exceptional alkaline overall water splitting performance of the electrode resulted from the high charge mobility at the interface that enhanced synergy between Y2Ru2O7 and NiMoO4. The results of this study show that combining the metal oxides Y2Ru2O7 and NiMoO4 is a promising approach for preparing materials with high catalytic activity for use in alkaline overall water splitting.

N self‐doped multifunctional chitosan biochar-based microsphere with heterogeneous interfaces for self-powered supercapacitors to drive overall water splitting

Due to the rising need for clean and renewable energy, green materials including biochar are becoming increasingly popular in the field of energy storage and conversion. However, the lack of highly active and stable electrode materials hinders the development of stable energy supplies and efficient hydrogen production devices. Herein, we fabricated stable, conductive, and multifunctional chitosan microspheres by a facile emulsion crosslinking solution growth and hydrothermal sulphuration methods as multifunctional electrodes for overall water splitting driven by supercapacitors. This material possessed three-dimensional layered conductors with favorable heterojunction interface, ample hollow and porous structures. It presented remarkably enhanced electrochemical and catalytic activity for both supercapacitors and overall water electrolysis. The asymmetric supercapacitors based on chitosan biochar microsphere achieved high specific capacitance (260.9 F g−1 at 1 A g−1) and high energy density (81.5W h kg−1) at a power density of 978.4 W kg−1. The chitosan biochar microsphere as an electrode for electrolyze only required a low cell voltage of 1.49 V to reach a current density of 10 mA cm−2, and achieved excellent stability with 30 h continuous test at 20 mA cm−2. Then, we assembled a coupled energy storage device and hydrogen production system, the SCs as a backup power source availably guaranteed the continuous operation of overall water electrolysis. Our study provides valuable perspectives into the practical design of both integrated biochar-based electrode materials and coupled energy storage devices with energy conversion and storage in practical.Graphical

Exclusively carbon-based self-supporting electrodes doped with different heteroatoms for overall water splitting in a wide pH range

Carbon-based electrocatalysts are considered as promising catalysts for water separation due to their earth-rich elements, low cost and high catalytic activity. Here, we construct an electrode system based on carbon materials consisting of carbon quantum dots (CQDs) doped with different heteroatoms are integrated on vertically aligned graphene array (VG) (X-VG-CQDs, X = N, S, P, B) as self-supporting electrodes for overall water splitting. The electrochemical performance shows the following pattern: N-VG-CQDs > S-VG-CQDs > P-VG-CQDs > B-VG-CQDs > VG-CQDs. DFT calculations are performed to investigate the correlation between electrochemical performances of various heteroatoms doped of VG-CQDs. The stability test results show that a series of heteroatom-doped VG-CQDs electrodes exhibit more than 50 h stability in a wide pH range. And the Faraday efficiencies of these electrodes for hydrogen evolution reaction are nearly 81%. This study may shed light on the development of efficient cost-effective carbon-based self-supporting electrodes for overall water splitting.

Interfacial engineering for promoting charge transfer in MoS2/CoFeLDH heterostructure electrodes for overall water splitting

In order to enhance the kinetics of water electrolysis and reduce the cell voltage, the development of highly active and stable non-precious metal bifunctional catalysts is essential. In this study, self-supported heterostructures based on MoS2-CoFeLDH were synthesised as the cathode and anode electrocatalysts for overall water splitting in alkaline media. The strong coupling effect at the heterogeneous interfaces of MoS2 and CoFeLDH improved the hydrogen evolution reaction (HER) at the cathode. The strong electronegativity of CoFeLDH facilitated the adsorption of H protons, and MoS2 with strong electrical conductivity promoted the desorption of H2 molecules. The oxygen evolution reaction (OER) at the anode was also enhanced because the LDHs had strong adsorption properties for hydroxyl species, and MoS2 assisted the transfer of hydroxyl species. The MoS2-CoFeLDH showed low overpotentials of 100 mV for the HER and 216 mV for the OER at 10 mA/cm2. This bifunctional catalyst required a low voltage of 1.55 V for overall water splitting and remained stable for 48 h.

Interfacial Coupling of Graphene with Nickel Nanoparticles for Water Splitting and Urea Oxidation: A Spectroelectrochemical Investigation.

Nickel nanoparticle and graphene interfaces of various stoichiometries were created through electrodeposition techniques. The catalytic behavior of the electrodeposited films was investigated through spectro-electrochemical methodologies. UV-vis absorbance spectra of the electrodeposited films are significantly different in the air and alkaline medium. Furthermore, UV-vis and Raman spectroscopy confirmed the coupling of Ni nanoparticles (Ni-NP) with the graphene framework, along with NiO and Ni(OH)2 . A combination of Raman and impedance spectroscopy revealed that the surface adsorption and charge transfer properties of the electrodeposited films are entirely dependent on the defects on graphene structure as well as distribution of Ni-NP on graphene. The electrodeposited films possess heterogeneous catalytic properties with a low overpotential of 50 mV (10 mA/cm-2 ) for hydrogen evolution reaction, as well as 601 mV and 391 mV (at 50 mA/cm-2 ) for the oxygen evolution reaction and urea oxidation reaction, respectively. In addition, eelectrodeposited samples show extraordinary overall water splitting performance by achieving a current density of 10 mA/cm2 at a very low applied potential of 1.38 V. This synergistic coupling of Ni and graphene renders the electrodeposited samples promising candidates as electrodes for overall water splitting in alkaline and urea-supplemented solutions.

A stable and robust electrode using Copious metal oxide composite for green hydrogen production

AbstractThe exploration of inexpensive and copious materials for water splitting has not come to an end even though a lot of materials has been synthesised to cope with the high overpotential and Tafel slope. The present manuscript demonstrates fabrication and performance studies of Co3O4 and TiO2 composite (CTC) catalyst coated electrode for electrochemical water splitting. The use of CTC (Co3O4@TiO2) showed the band gap of 2.41 eV which is found to be suitable for efficient water splitting reaction. The electrode fabrication was done using CTL coated FTO glass that provided a stable cathodic electrode for overall water splitting. The detail electrochemical studies of CTC electrode were performed in 1 M KOH electrolyte solution in a three‐electrode system. The CTC exhibited lowest Tafel slope value for both hydrogen evolution reaction (HER) of 51 mV/dec and oxygen evolution reaction (OER) of 166 mV/dec, calculated at 10 mA/cm2. Moreover, the highest current density 66.59 mA/cm2 at 0.20 V and 85.84 mA/cm2 at 1.85 V was observed for HER and OER, respectively. The significantly low overpotential 104 mV for HER and 240 mV for OER at 10 mA/cm2 depicted the efficiency of catalyst. The chronoamperometry study showed no significant loss in the activity CTC coating upto 32 h. Thus, the CTC coated electrode is found to be an excellent, stable and robust electrocatalyst for economical green H2 production.

Superhydrophilicity boron-doped cobalt phosphide nanosheets decorated carbon nanotube arrays self-supported electrode for overall water splitting

Transition metal borides (TMBs) or phosphides (TMPs) have attracted great attention to the design of bifunctional electrocatalysts for energy storage. The superaerophobicity and superhydrophilicity of the catalytic electrode surface are crucial factors to determine the reaction process of the gas electrode. Herein, we report a self-supported electrode of carbon nanotube (CNTs) array grown on carbon cloth (CC) modulated together by boron-doped cobalt phosphide (CoP-B/CNTs/CC). The electrode requires the overpotential of 73.8 mV and 189.5 mV at the current density of ±10 mA cm−2 for hydrogen and oxygen evolution reactions in an alkaline electrolyte (1.0 M KOH), respectively, meanwhile maintaining outstanding long-term durability for more than 300 h. The excellent activity of CoP-B/CNTs/CC is attributed to boron doping regulating its electronic structure and further enriching active sites. The attractive stability of CoP-B/CNTs/CC is due to the unique geometric structure of the self-supported electrode. Furthermore, the superaerophobicity and superhydrophilicity of the electrode surface also accelerate the reaction process of the gas electrode. Expectedly, water splitting cells assembled using CoP-B/CNTs/CC electrodes as cathode and anode, respectively, require a cell voltage of 1.54 V at 10 mA cm−2, which is lower than that of the Pt/C/CC||RuO2/CC couple (1.69 V at 10 mA cm−2). Importantly, CoP-B/CNTs/CC||CoP-B/CNTs/CC achieve stable cell voltage under the step current changes (10 mA cm−2, 50 mA cm−2, and 100 mA cm−2) over 300 h. This work highlights a new path to understanding the effects of the static and dynamic behavior of bubbles on the surface of self-supporting electrodes on catalytic performance.

Anchoring cobalt molybdenum nickel alloy nanoparticles on molybdenum dioxide nanosheets as efficient and stable self-supported catalyst for overall water splitting at high current density

Developing bifunctional electrocatalysts with efficient and stable catalytic performance at high current density to improve the productivity of water splitting is important for relieving the environmental pollution and energy crisis. Herein, the Ni4Mo and Co3Mo alloy nanoparticles were anchored on MoO2 nanosheets (H-NMO/CMO/CF-450) by annealing the NiMoO4/CoMoO4/CF (CF: self-made cobalt foam) under Ar/H2 atmosphere. Benefitting from the nanosheets structure, synergistic effect of the alloys, existence of oxygen vacancy and the cobalt foam with smaller pore sizes as conductive substrate, the self-supported H-NMO/CMO/CF-450 catalyst demonstrates outstanding electrocatalytic performance, which delivers small overpotential of 87 (270) mV at 100 (1000) mA·cm−2 for HER and 281 (336) mV at 100 (500) mA·cm−2 for OER in 1 M KOH. Meanwhile, the H-NMO/CMO/CF-450 catalyst is used as working electrodes for overall water splitting, which just require 1.46 V @ 10 mA·cm−2 and 1.71 V @ 100 mA·cm−2, respectively. More importantly, the H-NMO/CMO/CF-450 catalyst can stabilize for 300 h at 100 mA·cm−2 in both HER and OER. This research provides an idea for the preparation of stable and efficient catalysts at high current density.

Identifying Fe as OER Active Sites and Ultralow-Cost Bifunctional Electrocatalysts for Overall Water Splitting.

Electrocatalysts based on Fe and other transition metals are regarded as most promising candidates for accelerating the oxygen evolution reaction (OER), whereas whether Fe is the catalytic active site for OER is still under debate. Here, unary Fe- and binary FeNi- based catalysts, FeOOH and FeNi(OH)x , are produced by self-reconstruction. The former is a dual-phased FeOOH, possessing abundant oxygen vacancies (VO ) and mixed-valence states, delivering the highest OER performance among all the unary iron oxides- and hydroxides- based powder catalysts reported to date, supporting Fe can be catalytically active for OER. As to binary catalyst, FeNi(OH)x is fabricated featuring 1) an equal molar content of Fe and Ni and 2) rich VO , both of which are found essential to enable abundant stabilized reactive centers (FeOOHNi) for high OER performance. Fe is found to be oxidized to 3.5+ during the *OOH process, thus, Fe is identified to be the active site in this new layered double hydroxide (LDH) structure with Fe:Ni = 1:1. Furthermore, the maximized catalytic centers enable FeNi(OH)x @NF (nickel foam) as low-cost bifunctional electrodes for overall water-splitting, delivering excellent performance comparable to commercial electrodes based on precious metals, which overcomes a major obstacle to the commercialization of bifunctional electrodes: prohibitive cost.

Simple cathodic deposition of FeS/NiS-activated Ni/NiO heterojunctions for high-concentration overall water splitting reactions

To produce hydrogen through electrolysis of water, the creation of effective and affordable electrodes for overall water splitting is essential. We present the deposition of active oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) components on the same NF in this work, enabling the synergistic effect of FeS/NiS and Ni/NiO active components for effective overall water splitting. In alkaline electrolytes, NiFe@NF electrodes deposited using a straightforward two-step cathodic deposition process at various currents exhibit good catalytic activity for both OERs and HERs. For the electrode to be stable over time, Ni/NiO is firmly bonded to NF, and the specific surface areas of the FeS/NiS nanoflowers provide efficient electron transport. The electrode outperformed the RuO2 electrode by achieving a current density of 10 mA cm−2 at an OER overpotential of 168 mV. Additionally, the HER only needs a 84 mV overpotential to reach a current density of 10 mA cm−2. In addition, an electrolytic cell constructed with the same NiFe@NF as the cathode and anode requires a cell voltage of only 1.47 V to achieve a current density of 10 mA cm−2. It can operate stably for a long time (120 h) at high temperature and high concentration conditions. This work highlights the importance of active components with simultaneous OER and HER activities on electrodes for efficient catalytic applications in overall water splitting.

Electronic structure reconfiguration of nickel–cobalt layered double hydroxide nanoflakes via engineered heteroatom and oxygen-vacancies defect for efficient electrochemical water splitting

The development of earth-abundant and high-efficiency bifunctional electrocatalysts is extremely desirable for electrochemical water splitting, but there are some critical challenges that need to be addressed. The coordinated tailoring of electronic structure and Bader charge transference by heteroatom doping and oxygen vacancy defects are one of the strongest tactics to enhance the oxygen and hydrogen evolution reactions (OER and HER) of catalysts. Herein, a novel Mo-decorated nickel–cobalt layered double hydroxides 3D honeycomb nanoflake on Ni foam (labeled as Mo-NiCo LDHs(Vo)) as bifunctional electrode materials with enriched oxygen vacancy defects, excellent geometric stability, and enriched active sites was successfully fabricated through a facile hydrothermal reaction strategy. Density functional theory computations and experimental results confirmed that the electrocatalytic intrinsic activity of Mo-NiCo LDHs(Vo) was optimized not only because of the provision of new active sites by the Mo dopants via the construction of defects and oxygen vacancies but also because of the activation of the local electronic structures of the surrounding Ni and Co sites. Consequently, Mo-NiCo LDHs(Vo) exhibited outstanding electrocatalytic performance with an overpotential of 258 mV for OER and 194 mV for HER at a current density of 10 mA/cm2 in an alkaline medium. In addition, the catalyst exhibited excellent long-term stability after 100 h of use as a bifunctional electrode for overall water splitting. This work provides a facile means to fabricate superior, efficient noble metal-free catalysts with well-designed defects at the atomic-level using electronic structure engineering for energy-related applications.

A hierarchical cactus-like nanostructure as a bifunctional catalyst for overall water splitting

In this study, a hierarchical cactus-like nanostructure with cobalt doped iron disulfide (Co-FeS2) needle nanowires as trunks and nickel-iron layered double hydroxide (NiFe-LDH) nanosheets as branches was constructed as a self-supporting electrode for overall water splitting in alkaline electrolytes. A low electron density NiFe-LDH derived from the strong electronic interaction between sulfides and NiFe-LDH is remarkably effective in facilitating the adsorption of H2O and OH−, while the presence of Co atoms in FeS2 facilitates the hydrogen adsorption. Such a synergetic effect improved the HER performance in alkaline electrolytes significantly. In terms of the OER process, the Fe/Co oxyhydroxides produced from in situ phase transition from Co-FeS2 in conjunction with NiFe-LDH endow the electrode with excellent OER activity. Furthermore, the Co-FeS2 needle nanowires with metal-like conductivity allow for rapid electron transfer during electrochemical processes, and the hierarchical structure exposes substantial active sites and facilitates electrolyte penetration. In alkaline media, the electrode demonstrated outstanding HER and OER catalytic activity, requiring small overpotentials of 131 mV and 220 mV to reach current densities of 10 mA cm−2 and 20 mA cm−2, respectively. Moreover, it only needed 1.58 V to drive 10 mA cm−2 when utilized simultaneously as both cathode and anode for overall water splitting.

Ultra-thin hierarchical porous carbon coated metal phosphide self-assembled efficient tri-functional electrodes for overall water splitting and rechargeable zinc-air batteries

Highly efficient and stable trifunctional electrocatalysts with controllable nanostructures toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) are extraordinarily important for the sustainable energy development. Here we report a general and facile synthetic method for designing a hierarchically porous Ni-foam-based self-supported electrode (NPO/NixPy@NF-HPCs). Based on its unique design concept, the NPO/NixPy@NF-HPCs shows high tri-functional catalytic activities. As a result, the NPO/NixPy@NF-HPCs-based rechargeable zinc-air battery (ZAB) and water splitting device exhibit high power density up to 377 mW cm−2 and low cell voltage of 1.52 V@10 mA cm−2, respectively. Notably, the mapping between the stability and the quasi-in situ characterization demonstrates that it is a reliable method to improve electrode stability by establishing a stable outer carbon layer to avoid the oxidation of internally active sites. This work is promised to provide a viable new approach to developing efficient and low-cost carbon-supported phosphate tri-functional electrode.

Selenium anion substitution endows manganese sulfide as a bifunctional electrocatalyst for efficient water splitting in alkaline solutions

Currently, it is still highly desirable to develop high activity, cost-effective and stable electrocatalyst for accomplishing robust water splitting. Due to its excellent electroconductivity and large atomic ratio, transition metal sulfides or selenides have been extensively designed and highly-developed for the electrocatalysts field. Herein, a novel Tribulus terrestris like nanostructure MnSxSe1-x@N,F-CQDs nanocomposites with abundant defects was designed based on successive strategy including microwave-assisted heating, hydrothermal and calcination. Benefiting from its distinctive chemical structure and morphology, the as-developed MnSxSe1-x@N,F-CQDs possesses impressive electrocatalytic activities under alkaline condition with low overpotentials of 209 mV for oxygen evolution reaction (OER) and 87 mV for hydrogen evolution reaction (HER) at the current density of 10 mA cm−2, simultaneously yielding low Tafel slope of 72.18 and 78.19 mV dec−1. The MnSxSe1-x@N,F-CQDs also exhibits remarkable long-term stability. Importantly, when utilized as the bifunctional electrode for overall water splitting, the MnSxSe1-x@N,F-CQDs||MnSxSe1-x@N,F-CQDs merely requires an applied voltage of 1.55 V at 10 mA cm−2 and diplays prominent durability, which is almost comparable with that of the noble metal based RuO2‖Pt/C system. This work gains a new insight into the rational construction and exploration of inexpensive and high-efficient transition metal sulfides/selenides bifunctional electrocatalyst for overall water splitting by CQDs induction coupled with anionic substitution strategies.

Two-dimensional bimetallic Fe/M- (Ni, Zn, Co and Cu) metal organic framework as efficient and stable electrodes for overall water splitting and supercapacitor applications

2D based bimetallic MOFs have attracted significant attention for energy conversion and storage due to their synergistic effects and high electrocatalytic performance. However, the limited active sites and stability inhibit their multi-functional applicability in water electrolysis and supercapacitor applications. Herein, we report the 2D bimetallic Fe/M-BDC ((M-Ni, Zn, Co and Cu), BDC:1,4 benzene dicarboxylic acid) framework prepared by solvothermal and exfoliation condition, which exhibits excellent electrochemical performance. Electrochemical measurements and spectroscopic analysis establish that 2D Fe/M-BDC (M-Ni, Zn) contains a high surface area and abundant active sites that can accelerate the reaction kinetics. The as-prepared catalyst exhibits very low overpotentials of 78 mV for the hydrogen evolution reaction and 160 mV for the oxygen evolution reaction @ 10 and 20 mA cm−2, respectively. The bifunctional electrode assembly cell using anodic Fe/Zn-BDC and cathodic Fe/Ni-BDC couple provides the very low cell voltage of 1.35 V to drive current density of 10 mA cm−2. In addition, Fe/Zn-BDC and Fe/Ni-BDC exhibit high specific capacitances of 633.21 F/g and 1190.88 F/g at 1 mVs−1, respectively, with good stability when they are used as supercapacitor electrodes.