Phosphate ions-functionalized and wettability-tuned nickel ferrite for boosted oxygen evolution performance

Nickel ferrite (NiFe₂O₄) has been explored as a promising oxygen evolution reaction (OER) electrocatalyst for water splitting owning to its earth-abundant and considerable water oxidation catalytic activity. Nevertheless, its practical electrocatalytic performance towards OER is still undesirable due to the sluggish OER kinetics and high overpotential gap on the water oxidation anode side. In this work, in order to enhance the electrochemical water oxidation performance of NiFe₂O₄, the surface of NiFe₂O₄ is functionalized with phosphate ions (Pi) by using a facile incipient impregnation and following calcination process. Results demonstrate that the OER properties of NiFe₂O₄ under alkaline conditions can be dramatically boosted by the surface Pi functionalization. In 1.0 M KOH solution, the resulting NiFe₂O₄-Pi on glassy carbon (GC) electrode demonstrates quite lower overpotential of 332 mV (10 mA/cm²) and Tafel slope of 57 mV/dec compared to that of pristine NiFe₂O₄ (443 mV@10 mA/cm² and 96 mV/dec), which is also better than that of commercial RuO₂ electrocatalysts (348 mV@10 mA/cm² and 80 mV/dec). Moreover, such electrocatalyst on nickel foam electrode also realizes superior OER durability to afford a current density of 70 mA/cm² at overpotential of only 300 mV for at least 28 h. The excellent electrocatalytic water oxidation activities of NiFe₂O₄-Pi can be attributed to the tuning electronic property and surface wettability by Pi ions functionalization. This work provides us a novel and effective approach to modify the photo-/electrocatalytic activity for transition metal oxides.     

Three-dimensional Ni/Fe doped graphene oxide @ MXene architecture as an efficient water splitting electrocatalyst

Developing a highly efficient, stable, and earth-abundant electrocatalyst for both HER and OER is essential for water splitting. Herein, we report a bifunctional electrocatalyst in the form of iron/nickel doped graphene oxide @ MXene (GMX). The GMX-based electrocatalytic materials were prepared by annealing at different temperatures in an inert atmosphere. The GMX was characterized by various analytical tools such as PXRD, FE-SEM, HRTEM, Raman spectroscopy, and XPS. All the electrocatalysts exhibit high activity when acting as OER and HER catalyst in alkaline and acidic electrolytes. GMX-500 is considered an effective bifunctional electrocatalyst, and 10 mA cm^?2 current density is achieved at a low overpotential, i.e., 370 mV for OER and 470 mV for HER, respectively. This paper focuses on the progress of inexpensive and effective electrocatalysts with high activity and long-term durability for water splitting, which is relevant in power conservation.     

Electrodeposited Ni-Co-Sn alloy as a highly efficient electrocatalyst for water splitting

Water splitting to produce hydrogen and oxygen is considered as a feasible solution to solve the current energy crisis. It is highly desirable to develop inexpensive and efficient electrocatalyst for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this paper, nanostructured Ni-Co-Sn alloys were electrodeposited on copper foil and the excellent electrocatalytic performances for both HER and OER in alkaline media were achieved. The optimized Ni-Co-Sn electrode shows a low onset overpotential of −18 mV and a small Tafel slope of 63 mV/dec for the HER, comparable to many state-of-the-art non-precious metal HER catalysts. For the OER, it produces an overpotential of 270 mV (1.50 V vs. RHE) at current density of 10 mA/cm², which is better than that of the commercial Ir/C catalyst. In addition to high electrocatalytic activities, it exhibits good stability for both HER and OER. This is the first report that Ni-Co-Sn is served as a cost-effective and highly efficient bifunctional catalyst for water splitting and it will be of great practical value.     

Effect of cation substitution in MnCo2O4 spinel anchored over rGO for enhancing the electrocatalytic activity towards oxygen evolution reaction (OER)

Developing an efficient and durable electrocatalyst for catalyzing oxygen evolution reaction in electrochemical water splitting application is greatly desired and challenging. Herein, a simple and facile strategy was followed to prepare Ni-substituted MnCo₂O₄/rGO nanocomposite as an electrocatalyst for oxygen evolution reaction (OER). The structural and morphological analyses show the successful bonding between spinel-carbon hybrid. Nickel substitution and addition of rGO disclose a drastic change in the catalytic activity of the same towards OER. Among all the electrocatalysts, Mn_1-xNi_xCo₂O₄/rGO with x = 0.6 exhibits low overpotential of 250 and 290 mV for attaining the current density of 10 mA/cm² before and after potential cycling respectively. It also exhibits low onset potential of 1.48 V with a Tafel slope of value 78 mV/dec. The electrocatalyst also shows excellent stability, high ECSA and roughness factor (R_f) which are responsible for enhanced OER performance. These properties confirm that the present hybrid material would be an excellent electrocatalyst for catalyzing OER for hydrogen energy production.     

Amorphous CoFeP/NC hybrids as highly efficient electrocatalysts for water oxidation

The rational design and regulate structure and composition are pivotal for the development of highly efficient oxygen evolution reaction (OER) catalysts for water splitting. In this study, amorphous CoFeP/NC hybrid electrocatalyst has been synthesized by a simple and effective phosphorization of a CoFe-based coordination polymer under N₂ atmosphere. The synergistic effects between the CoFeP and N-doped carbon has led to high electronic conductivity attributed to the optimal Fe contents with N-doped carbon and enlarged electrocatalytic active surface area aroused by the nanostructure of CoFeP/NC, as well as the surface structural evolution of oxyhydroxide/phosphate during OER process. The resulting Co_0.35Fe_0.17P_0.48/NC electrocatalyst can attain a current density of 10 mA/cm² at an overpotential of 275 mV with a Tafel slope of 31 mV/dec on glassy carbon electrode and 228 mV on Ni foam electrode in 1 M KOH solution, long-term OER stability of this Co_0.35Fe_0.17P_0.48/NC under the applied potential of 1.53 V vs. RHE demonstrates no obvious decline in current densities of 110 mA/cm² within 17 h, which outperforms those of the contrast electrocatalysts in this work and also comparable to that of many of the reported electrocatalysts in the literatures. This Co_0.35Fe_0.17P_0.48/NC electrocatalyst highlights the rational modulation of optimal composition and electronic structure with homogeneous incorporation of the foreign metal-doped and N-doped carbon for the synthesis of highly efficient electrocatalysts toward to the water oxidation reactions.     

Porous sunflower plate-like NiFe2O4/CoNi–S heterostructure as efficient electrocatalyst for overall water splitting

Constructing high-efficient and nonprecious electrocatalysts is of primary importance for improving the efficiency of water splitting. Herein, a novel sunflower plate-like NiFe₂O₄/CoNi–S nanosheet heterostructure was fabricated via facile hydrothermal and electrodeposition methods. The as-fabricated NiFe₂O₄/CoNi–S heterostructure array exhibits remarkable bifunctional catalytic activity and stability toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. It presents a small overpotential of 219 mV and 149 mV for OER and HER, respectively, to produce a current density of 10 mA cm^?2. More significantly, when the obtained electrodes are used as both the cathode and anode in an electrolyzer, a voltage of 1.57 V is gained at 10 mA cm^?2, with superior stability for 72 h. Such outstanding properties are ascribed to: the 3D porous network structure, which exposes more active sites and accelerates mass transfer and gas bubble emission; the high conductivity of CoNi–S, which provides faster charge transport and thus promotes the electrocatalytic reaction of the composites; and the effective interface engineering between NiFe₂O₄ (excellent performance for OER) and CoNi–S (high activity for HER), which leads to a shorter transport pathway and thus expedites electron transfer. This work provides a new strategy for designing efficient and inexpensive electrocatalysts for water splitting.     

Highly efficient overall water splitting performance of gadolinium-indium-zinc ternary oxide nanostructured electrocatalyst

Metal oxide nanostructures gain specific interest for bifunctional electrocatalytic functions in efficient water splitting reactions. From this perspective, Gd-In-Zn-based ternary oxides were solution processed and studied for oxygen and hydrogen evolution activities under different pH alkaline media. The nanostructure morphology was ascertained using high-power analytical tools such as scanning and transmission electron microscopes. Signals obtained from X-ray diffraction data revealed the prevalence of Gd₂O₃ phase in ternary oxide. Valence state of Gd, In, and Zn ions and their oxide traits was examined using X-ray photoelectron spectroscopy. Ternary oxides of Gd-In-Zn showcased their overall potential for water splitting applications. Overpotential (η) for oxygen and hydrogen (OER/HER) evolution reactions was recorded to be 282 and 271 mV for ±10 mA/cm². The results demonstrated the processed oxide as an effective OER/HER electrocatalyst with profound Tafel slopes (121/64 mV/dec for OER/HER) and excellent long-term stability.     

Three-dimensional hierarchically porous iridium oxide-nitrogen doped carbon hybrid: An efficient bifunctional catalyst for oxygen evolution and hydrogen evolution reaction in acid

Active and durable acid medium electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are of critical importance for the development of proton exchange membrane (PEM) water electrolyser or Fuel cells. Herein, we report a facile method for the synthesis of 3D-hierarchical porous iridium oxide/N-doped carbon hybrid (3D-IrO₂/N@C) and its superior OER and HER activity in acid. In 0.5 M HClO₄, this catalyst exhibited remarkable activity towards OER with a low overpotential of 280 mV at 10 mA/cm² current density, a low Tafel slope of 45 mV/dec and ∼98% faradaic efficiency. The mass activity (MA) and turnover frequency (TOF) are found to be 833 mA/mg and 0.432 s⁻¹ at overpotential of 350 mV which are ∼32 times higher than commercial (comm.) IrO₂. The HER performance of this 3D-IrO₂/N@C is comparable with comm. Pt/C catalyst in acid. This 3D-IrO₂/N@C catalyst requires only 35 mV overpotential to reach a current density 10 mA/cm² with Tafel slope 31 mV/dec. Most importantly, chronoamperometric stability test confirmed superior stability of this catalyst towards HER and OER in acid. This 3D-IrO₂/N@C catalyst was applied as both cathode and anode for over-all water splitting and required only 1.55 V overpotential to achieve a current density of 10 mA/cm² in acid. The outstanding activity of the 3D-IrO₂/N@C catalyst can be attributed to a unique hierarchical porous network, high surface area, higher electron and mass transportation, synergistic interaction between IrO₂ and carbon support.     

Extraordinarily high hydrogen-evolution-reaction activity of corrugated graphene nanosheets derived from biomass rice husks

The metal-free carbonaceous catalysts are one of the promising candidates for efficient electrocatalytic hydrogen production. Aiming at demonstrating the high electrocatalytic activity of the hydrogen evolution reaction (HER), we synthesized the biomass rice husk-derived corrugated graphene (RH-CG) nanosheets via the KOH activation. The 700 °C-activated RH-CG nanosheets exhibited the large specific surface area as well as the high electrical conductivity. When using the RH-CG nanosheets as a HER electrocatalyst in 0.5 M H₂SO₄, the excellent HER activities with a small overpotential (9 mV at 10 mA/cm²) and a small Tafel slope (31 mV/dec) were achieved. The results provide a new strategy for materializing the superb biomass-derived electrocatalyst for highly efficient hydrogen production.     

Evidencing enhanced oxygen and hydrogen evolution reactions using In–Zn–Co ternary transition metal oxide nanostructures: A novel bifunctional electrocatalyst

Ternary transition metal oxides are gaining popularity for cost effective bifunctional electrocatalytic activities and to realization of novel water splitting devices. In this regard, In₂O₃/ZnO/Co₃O₄ based ternary oxide nanostructures were investigated in detail for their oxygen/hydrogen evolution reaction (OER/HER) in alkaline environment. The ternary oxides were at first processed through a simple chemical route involving hydrothermal treatment. The prepared nanostructures were then investigated by using high-resolution transmission electron microscopy (TEM/HRTEM) to ascertain their morphological traits. X-ray diffraction, Raman signals and photoluminescence data demonstrated the In₂O₃ phase to be prevalent in the ternary mixture on par with that of ZnO and Co₃O₄. The valence state of various metal ions and the In–O, Zn–O and Co–O bonding was verified using XPS. The ternary oxide coated electrodes exhibited excellent overall water splitting activity. Overpotential values of 398 and 510 mV were registered for OER and HER experiments under a current density of ±10 mA cm⁻², demonstrating the material to be an ideal OER/HER electrocatalyst at room temperature. The exceptional long-term stability in ternary oxides and their Tafel slope (88 mV/dec for OER and 60 mV/dec for HER) further affirmed their unique anodic/cathodic characteristics for water splitting applications.     

Overall noble metal free Ni and Fe doped Cu2ZnSnS4 (CZTS) bifunctional electrocatalytic systems for enhanced water splitting reactions

Herein, we report an inexpensive synthesis of sonochemical nickel and iron (M = Ni, Fe) doped Cu₂ZnSnS₄ (CZTS) and their utility as a nanoelectrodes for improved electrocatalytic water splitting performance. The as-synthesized electrode materials were characterized further by Transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman and X-ray photoelectron (XP) spectroscopic studies. Significantly, Ni doped CZTS electrocatalyst exhibits low overpotential approximately 214 and 400 mV for the hydrogen evolution reactions (HER) in 0.5 M H₂SO₄ and 1 M KOH electrolyte solutions respectively, and 1.29 V vs RHE for the oxygen evolution reactions (OER) in 1 M KOH at 10 mA/cm² current density. Small Tafel slopes and tested durability for longer time i.e. upto 500 min for water splitting, demonstrates that Ni doped CZTS is efficient bifunctional electrocatalyst having high activity along with extraordinary current/potential stability. Moreover, Fe doped CZTS electrocatalyst shows relatively poor response, i.e. overpotential 300 mV in 0.5 M H₂SO₄ and 445 mV in 1.0 M KOH towards HER and overpotential 1.54 V for the OER in 1 M KOH reaches at 10 mA/cm². This highly efficient bifunctional electrocatalysts that can meet the existing energy anxiety.     

Ni3S2-MoSx nanorods grown on Ni foam as high-efficient electrocatalysts for overall water splitting

In order to solve the problem of large overpotential in water electrolysis for hydrogen production, transition metal sulfides are promising bifunctional electrocatalysts for hydrogen evolution reaction/oxygen evolution reaction that can significantly reduce overpotential. In this work, Ni₃S₂ and amorphous MoS_x nanorods directly grown on Ni foam (Ni₃S₂-MoS_x/NF) were prepared via one-step solvothermal process, which were used as a high-efficient electrocatalyst for overall water splitting. The Ni₃S₂-MoS_x/NF composite exhibits very low overpotentials of 65 and 312 mV to reach 10 mA cm⁻² and 50 mA cm⁻² in 1.0 M KOH for HER and OER, respectively. Besides, it exhibits a low Tafel slope (81 mV dec⁻¹ for HER, 103 mV dec⁻¹ for OER), high exchange current density (1.51 mA cm⁻² for HER, 0.26 mA cm⁻² for OER), and remarkable long-term cycle stability. This work provides new perspective for further the development of highly effective non-noble-metal materials in the energy field.     

Nitrogen and nitrogen-sulfur doped graphene nanosheets for efficient hydrogen productions for HER studies

Carbon based electrocatalysts are promising candidates to achieve the production of hydrogen energy in a sustainable wayby simple water splitting technique. Thermally treated reduced graphene oxide (RGO) and N–S doped RGO employing urea and thiourea as electrocatalysts for hydrogen evolution reaction (HER). The performance of electrochemical HER has been thoroughly examined via linear sweep voltammetry, electrochemical impedance spectroscopy and chronoamperometry. Furthermore, the Raman I_D/I_G ratio of RGO, N-RGO and NS-RGO were found to be 1.43, 1.10 and 1.11 respectively. From electrochemical HER analysis, we found that the NS-doped RGO exposed the low overpotential, low Tafel slope and low solution resistance value of 211 mV, 197 mV/dec and 0.34 Ω respectively. In addition, the chronoamperometry study revealed, the electrocatalyst NS-RGO showed an excellent stability (81.3% retention) with low 211 mV and remained unchanged for more than 16 h. Therefore, this work concludes that heteroatom dopant participate in improving electrocatalytic HER action.     

Electrochemical construction of Cu@NF frameworks and synthesis of self-supported microflower Cu2S@NF as bifunctional catalysts for overall water splitting

A two-step electrochemical method is proposed for the in-situ deposition of copper and synthesis of copper(Ⅰ) sulfide (Cu₂S) with controllable morphology on nickel foam (NF), and the thus-prepared self-supported Cu₂S@NF electrodes exhibit excellent performance as bifunctional electrocatalysts. Characterizations with scanning electron microscopy show rock-shape of the deposited copper through potentiostatic method, which can be further sulfurized to microflower morphology by a unique underpotential electrochemical method. The size and amount of the deposits can be adjusted by controlling applied potentials, leading to the optimization of electrocatalytic activity. The Cu₂S@NF exhibits superior electrocatalytic performance towards HER and OER in 1 M KOH with the low overpotentials of 105 mV and 194 mV at 10 mA/cm², as well as small Tafel slopes of 92.89 mV/dec and 72.81 mV/dec, respectively. This work provides a simple method for the synthesis of efficient catalysts, which can be extended to the fabrication of other transition metal-based electrocatalysts.     

Thin-film iron-oxide nanobeads as bifunctional electrocatalyst for high activity overall water splitting

Developing only Fe derived bifunctional overall water splitting electrocatalyst both for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) while performing at low onset overpotential and with high catalytic stability is a rare instance. We present here the first demonstration of unique iron-oxide nanobeads (FeO_x-NBs) based electrocatalyst executing both OER and HER with high activity. Thin-film electrocatalytic FeO_x-NBs assembly is surface grown via simple spray coating (SC). The unique SC/FeO_x-NBs propels OER initiating water oxidation just at 1.49 V_RHE (η = 260 mV) that is the lowest observable onset potential for OER on simple Fe-oxide based catalytic films reported so far. Catalyst also reveals decently high HER activity and competent overall water splitting performance in the FeO_x-NBs two-electrode system as well. Catalyst also presents stable kinetics, with promising high electrochemically active surface area (ECSA) of 1765 cm², notable Tafel slopes of just 54 mV dec^1? (OER) and 85 mV dec^1? (HER), high exchange current density of 1.10 mA cm^2? (OER), 0.58 mA cm^2? (HER) and TOF of 74.29s^1?@1.58V_RHE, 262s^1?@1.62V_RHE (OER) and 82.5s^1?@-0.45V_RHE, 681s^1?@-0.56V_RHE (HER).     

Nickel foam-supported Fe,Ni-Polyporphyrin microparticles: Efficient bifunctional catalysts for overall water splitting in alkaline media

Developing highly active, stable and sustainable electrocatalysts for overall water splitting is of great importance to generate renewable H₂ for fuel cells. Herein, we report the synthesis of electrocatalytically active, nickel foam-supported, spherical core-shell Fe-poly(tetraphenylporphyrin)/Ni-poly(tetraphenylporphyrin) microparticles (FeTPP@NiTPP/NF). We also show that FeTPP@NiTPP/NF exhibits efficient bifunctional electrocatalytic properties toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Electrochemical tests in KOH solution (1 M) reveal that FeTPP@NiTPP/NF electrocatalyzes the OER with 100 mA cm⁻² at an overpotential of 302 mV and the HER with 10 mA cm⁻² at an overpotential of 170 mV. Notably also, its catalytic performance for OER is better than that of RuO₂, the benchmark OER catalyst. Although its catalytic activity for HER is slightly lower than that of Pt/C (the benchmark HER electrocatalyst), it shows greater stability than the latter during the reaction. The material also exhibits electrocatalytic activity for overall water splitting reaction at a current density of 10 mA cm⁻² with a cell voltage of 1.58 V, along with a good recovery property. Additionally, the work demonstrates a new synthetic strategy to an efficient, noble metal-free-coordinated covalent organic framework (COF)-based, bifunctional electrocatalyst for water splitting.     

Pomegranate-like Ni-doped cobalt boride implanted in B,N-doped carbon nanocages for enhanced electrochemical oxygen evolution

The development of efficient and stable transition metal boride electrocatalysts for oxygen evolution reaction (OER) is critical for energy conversion and environmental protection. Herein, we synthesized B, N-doped carbon layer encapsulated the Ni-doped Co_xB nanocages electrocatalyst (denoted as Ni-Co_xB@BNC) via a high-temperature boronizing, derived from Ni-doped cobalt-based zeolite imidazole frame (NiCo-ZIF), toward enhanced electrochemical alkaline oxygen evolution reaction. The Ni-Co_xB@BNC electrocatalyst synthesized at 550 °C exhibits excellent OER activity with a low overpotential of 274 mV and a Tafel slope of 80 mV dec⁻¹ at a current density of 10 mA cm⁻², which is better than precious metal RuO₂. The synergistic effect between B, N-doped carbon layer and Ni-doped Co_xB in Ni-Co_xB@BNC leads to higher OER catalytic activity. The B, N-doped carbon layer provides additional active sites, which accelerates charge transport and enhances the conductivity of Ni-Co_xB@BNC during OER. In addition, it also protects the pomegranate seed-like Ni-Co_xB nanoparticles inside, improving the stability of the Ni-Co_xB@BNC material. This work unambiguously elucidates the design and preparation strategy of transition metal boride implanted B, N-doped carbon nanocage electrocatalysts derived from controlled bimetallic ZIF precursor.     

Functionalization of Mn2O3/PdO/ZnO electrocatalyst using organic template with accentuated electrochemical potential toward water splitting

In a broad spectrum of renewable energy technologies, nonprecious, cheap, and robust electrocatalytic material is the fundamental element for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, designing high-efficiency catalysts to match industrial requirements remains a significant challenge. An Efficient and stable OER catalyst [Mn₂O₃/PdO/ZnO] was prepared by a simple and cost-effective facile synthesis approach using metal acetates with the organic extract. The carbonaceous material help in improving the surface area and lowering the band gap energy (2.2 eV) of the Mn₂O₃/PdO/ZnO suggesting the enhanced electrochemical conductivity of synthesized nanomaterial. The catalyst was loaded on Ni-foam and has been tested for Oxyge evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline medium. The material shows higher activity toward OER with a low overpotential and Tafel slope value of 93 mV/dec at a bias of 1.65 V to achieve a current density of 10 mA/cm². The material exhibited an overpotential of 57 mV and Tafel value of 244 mV/dec toward HER which were not much satisfactory. The material offer an overpotential value of 422 mV toward OER which remains consistent even after 2000 cycle in 1M KOH electrolyte. In addition, chronoamperometry test also revealed constant oxygen evolution over 24 hours without any loss in activity. Thus the synthesized bio-fabricated composite material is simple and scalable for widespread use in renewable energy harvesting applications.     

An efficient Fe2O3/FeS heterostructures water oxidation catalyst

Slow kinetics and insufficient understanding of the perceptual design of oxygen evolution reaction (OER) electrocatalysts are major obstacles. Overcoming these challenges, heterostructures have recently attracted attention because they encourage alternative OER electrocatalysts with active structural features. In this study, synthesis, characterization and electrochemical evaluation of the heterostructure of iron oxide/iron sulfide (Fe₂O₃/FeS) and its counterparts, iron oxide (Fe₂O₃) and iron sulfide (FeS) are reported. The structural features of as-synthesized electrocatalysts have been evaluated by infrared spectroscopy, powder X-ray diffraction study and scanning electron microscopy. Fe₂O₃/FeS was found to be a stable electrocatalyst for efficient water splitting, which initiates OER at a surprisingly low potential of 1.49 V (vs RHE) in 1 M potassium hydroxide. The Fe₂O₃/FeS electrocatalyst drives OER with a current density of 40 mA cm^?2 at overpotential of 370 mV and a Tafel slope of 90 mV dec^?1. Its performance is better than its counterparts (Fe₂O₃ and FeS) under similar electrochemical conditions. At an applied potential of 1.65 V (vs RHE), continuous oxygen production for several hours revealed the long-term stability and effective activity of the Fe₂O₃/FeS electrocatalyst for OER. The as-developed Fe₂O₃/FeS heterostructure provides an effective alternative low-cost metal-based electrocatalysts for OER.     

Ni(II) supramolecular gel-derived Ni(0) nanoclusters decorated with optimal N,O-doped graphitized carbon as bifunctional electrocatalysts for oxygen and hydrogen evolution reactions

Developing bifunctional, inexpensive and scalable electrocatalyst for both oxygen and hydrogen evolution reactions (OER and HER) is of essence, considering the thrust for clean fuel hydrogen, and the association of OER with several renewable energy systems, including metal-air batteries. A systematic understanding of electrocatalysts based on the amount and speciation of heteroatom doping on the carbon matrix is fundamental to catalyst design, but remains rarely investigated. This work presents the controlled synthesis of a series of homogeneously dispersed Ni nanoclusters confined in multiple layers of heteroatom-doped graphitized carbon, from the pyrolysis of a readily preparable Ni(II)-triazole gel. The best catalyst showed superior activity requiring low overpotentials of 360 mV & 250 mV and Tafel slopes of 69 mV dec^?1 & 115 mV dec^?1 for OER and HER respectively, with prolonged stability under challenging electrocatalytic conditions. Judicious modulation of the type of heteroatom dopants on Ni@N,O-doped carbon redistributed the electron-density and provided additional active sites, which assisted the adsorption/desorption of OER and HER intermediates during electrocatalysis and improved electron conductivity, benefitting both OER and HER. Our results highlight a simplistic approach for the meticulous synthesis of bifunctional electrocatalysts from supramolecular metallogels, opening new horizons for designing materials for energy applications.