Tafel Slope Value Research Articles

Non-Kinetic Effects Convolute Activity and Tafel Analysis for the Alkaline Oxygen Evolution Reaction on NiFeOOH Electrocatalysts.

A large variety of nickel-based catalysts has been investigated for the oxygen evolution reaction (OER) in alkaline media. However, their reported activity, as well as Tafel slope values, vary greatly. To understand this variation, we studied electrodeposited Ni80 Fe20 OOH catalysts with different loadings at varying rotation rates, hydroxide concentrations, with or without sonication. We show that, at low current density (<5 mA cm-2 ), the Tafel slope value is ≈30 mV dec-1 for Ni80 Fe20 OOH. At higher polarization, the Tafel slope continuously increases and is dependent on rotation rate, loading, hydroxide concentration and sonication. These Tafel slope values are convoluted by non-kinetic effects, such as bubbles, potential-dependent changes in ohmic resistance and (internal) OH- gradients. As best practise, we suggest that Tafel slopes should be plotted vs. current or potential. In such a plot, it can be appreciated if there is a kinetic Tafel slope or if the observed Tafel slope is influenced by non-kinetic effects.

Non‐Kinetic Effects Convolute Activity and Tafel Analysis for the Alkaline Oxygen Evolution Reaction on NiFeOOH Electrocatalysts

AbstractA large variety of nickel‐based catalysts has been investigated for the oxygen evolution reaction (OER) in alkaline media. However, their reported activity, as well as Tafel slope values, vary greatly. To understand this variation, we studied electrodeposited Ni80Fe20OOH catalysts with different loadings at varying rotation rates, hydroxide concentrations, with or without sonication. We show that, at low current density (&lt;5 mA cm−2), the Tafel slope value is ≈30 mV dec−1 for Ni80Fe20OOH. At higher polarization, the Tafel slope continuously increases and is dependent on rotation rate, loading, hydroxide concentration and sonication. These Tafel slope values are convoluted by non‐kinetic effects, such as bubbles, potential‐dependent changes in ohmic resistance and (internal) OH− gradients. As best practise, we suggest that Tafel slopes should be plotted vs. current or potential. In such a plot, it can be appreciated if there is a kinetic Tafel slope or if the observed Tafel slope is influenced by non‐kinetic effects.

Tailoring of 1T Phase-Domain MoS2 Active Sites with Bridging S22–/Apical S2– Phase-Selective Precursor Modulation for Enriched HER Kinetics

Molybdenum disulfide (MoS2) is a promising alternative electrocatalyst for hydrogen evolution reaction (HER) due to its relatively near zero hydrogen adsorption free energy (ΔGH = 0.08) and availability as a metallic (1T) phase. The superior catalytic activity of the 1T phase over 2H is owing to the availability of dense active sites, 107 fold higher conductivity, and greater hydrophilicity. However, in the synthesis of 1T-MoS2, a highly controlled proficient method is indispensable due to its metastable nature. Besides, phase enrichment is greatly sensitive to experimental parameters such as precursor, temperature, reaction time, and solvent. In the context of precursors, to date, no single precursor has been recognized as a selective precursor for the synthesis of 1T-MoS2. In this work, MoS2 with high content of 1T phase (79.4%) and excessive bridging S22-/apical S2- sites has been formulated from a single precursor, that is, ammonium tetrathiomolybdate ((NH4)2MoS4), ATTM). In HER, it displayed an inspired activity, that is, achieving 10 mA cm-2 current density, it requires just 248 mV overpotential with a minimal Tafel slope value (56 mV/dec). The maximum enrichment of the 1T phase, abundant accumulation of catalytically active bridging S22-/apical S2- sites, and the complete reduction of Mo+6 to Mo+4 (absence of Mo+6) are root causes for the outstanding activity of the synthesized 1T phase-domain MoS2. To the best of our knowledge for the very first time, here, we declare that the single source, that is, ATTM is an exclusive precursor for the selective synthesis of 1T-MoS2 with advantageous structural features. Moreover, this expedient precursor could be more pertinent for the industrial-scale preparation of 1T phase-domain MoS2 in near future.

Collectively exhaustive electrochemical hydrogen evolution reaction of polymorphic cobalt selenides derived from organic surfactants modified Co-MOFs

Finding and exploring non-noble metal-based electrocatalysts for the promising power-to-hydrogen fuel technology through water splitting reactions is highly emerging. Herein, we report the preparation of cobalt-based metal-organic frameworks (Co-MOFs) using an oleylamine (OLA) and 1-dodecanethiol (DDT)-modified trimesic acid (TMA), and cobalt precursor. Then, the electrocatalytically active cobalt selenides were derived from the Co-MOFs by a water-organic solvent mixture-assisted single-step selenization process. Interestingly, the cobalt selenide obtained from the DDT-modified Co-MOF shows collectively exhaustive hydrogen evolution reaction (HER) performance with very small overpotentials of ∼161 and ∼206 mV to achieve 10 and 50 mA cm−2, respectively, due to the phase mixing characteristics of cobalt selenide and the synergistic interaction. The fast reaction kinetics were identified at the DDT-Co selenide electrode surface as confirmed by observing the lower charge-transport/interfacial resistance and Tafel slope value due to the high surface coverage of adsorbed hydrogen (Hads) atoms, evidenced by high interfacial chemical capacitance value, as a result of the high electrical conductivity and large electrochemically accessible active sites. The calculated activation energy (Ea) of HER further reveals a low kinetic energy barrier in the HER on the DDT-Co selenide, indicating high intrinsic catalytic activity due to the fast surface diffusion rate of Hads. Furthermore, the obtained cathodic transfer coefficient (αc) value strongly suggested that the HER on the surface of DDT-Co selenide (αc = 2) proceeds in the Langmuir-Hinshelwood reaction mechanism and follows the Volmer-Tafel pathway. The present work provides valuable insights into the modification of Co-MOFs and their impact on HER catalytic activity of cobalt selenide, and also the mechanistic investigation of HER based on electrochemical impedance spectroscopy analysis.

Slow O–H Dissociation in the First-Order Oxygen Evolution Reaction Kinetics on Polycrystalline γ-FeO(OH)

To unravel the reaction mechanism of the electrochemical oxygen evolution reaction (OER), analysis of the intrinsic activity parameters obtained via electrokinetic investigation remains effective. In this study, polycrystalline γ-FeO(OH), synthesized at room temperature, was used as a stable, albeit reactive, anode for OER, and electrokinetic studies were performed to unravel the oxygen evolution reaction pathway. The cell temperature, hydroxyl ion concentration, and the cation of the supporting electrolyte were varied, and the influence of external bias on the OER activity was recorded. Changes in the cell temperature from 30 to 65 °C lead to an enhanced OER activity due to small overpotential, Tafel slope, and charge-transfer resistance (Rct) values at high temperatures, which unambiguously highlights the influence of the thermodynamic barrier and electron-transfer kinetics. The calculated anodic charge-transfer coefficient (αa) and specific exchange current density (j0,s) values are 0.65 and 2.24 × 10–5 mA cm–2, respectively. The faster OER kinetics on polycrystalline γ-FeO(OH) can also be attributed to an appreciably low activation energy of 8.26 ± 2 kJ mol–1, where variation of the electrolyte concentration indicated a first-order dependence on [OH]−. Experimentally obtained intrinsic kinetic parameters such as the Tafel slope, anodic charge-transfer coefficient, exchange current density, activation energy (Ea), reaction order (m), and deuterium isotope effect implicate the dissociation of hydroxyl ions on the polycrystalline γ-FeO(OH) as the rate-determining step. The direct effect of cations such as Li+, Na+, and K+ of the electrolyte on OER highlights a weak interaction of the cations with the surface-active [FeIII-OH] species. A change in the electrode substance from three-dimensional highly conductive nickel foam (NF) to two-dimensional less conductive carbon cloth (CC) resulted in a change in the slow step, leading to the formation of a high-valency iron oxo intermediate from the iron hydroxy species.

Fatigue free relaxor ferroelectric and electrocatalytic hydrogen evolution of yttrium substituted BaBi2Nb2O9 layered structured nanoceramics for energy storage application

Lead-free bismuth layered structured ferroelectric ceramics are highly important in superior energy storage applications. The slim hysteresis curve with high energy storage density and efficiency is expected for wide application. In this regard, the suitable electrocatalyst for the generation of hydrogen gas through water-splitting show high importance as an alternative energy source. The current article aims to investigate the above goals by incorporating 5% yttrium at the place of bismuth for BaBi 2 Nb 2 O 9 relaxor ferroelectrics. The solid-state synthesized method successfully prepared the single-phase material and is confirmed through spectroscopic and morphological analysis. The dielectric characteristics follow diffused phase transition with broad temperature dependence that indicated the space charge polarization in the material owing to the presence of Y 3+ at different domains. The higher degree of diffuseness and low dielectric loss implies the significant role of charge carriers during frequency and temperature variation in the dielectric study. Impedance spectroscopy analysis indicates the non-Debye type relaxation and NTCR behavior of the material that is correlated to the multiple relaxation processes. The slim P-E hysteresis curve and fatigue-free properties of the materials up to 10 6 cycles reflect its usefulness in the potential device as NVRAM applications. The materials are also used for hydrogen evolution reaction (HER) under an electrochemical condition. A lower overpotential value of 180 mV is obtained at 10 mA cm −2 current density. The lower Tafel slope and charge transfer resistance value support its superior HER activity. The above results demonstrated the potential application of the studied material (BaBi 1 · 9 Y 0 · 1 Nb 2 O 9 ) in the energy storage application and as an electrocatalyst for alternative energy source.

NiCo2O4 nano-needles as an efficient electro-catalyst for simultaneous water splitting and dye degradation.

Developing an efficient and non-precious bifunctional catalyst capable of performing water splitting and organic effluent degradation in wastewater is a great challenge. This article reports an efficient bifunctional nanocatalyst based on NiCo2O4, synthesized using a simple one-pot co-precipitation method. We optimized the synthesis conditions by varying the synthesis pH and sodium dodecyl sulfate (SDS) concentrations. The prepared catalyst exhibited excellent catalytic activity for the electrochemical oxygen evolution reaction (OER) and simultaneous methylene blue (MB) dye degradation. Among the catalysts, the catalyst synthesized using 1 g SDS as a surfactant at 100 °C provided the highest current density (658 mA cm-2), lower onset potential (1.34 V vs. RHE), lower overpotential (170 mV @ 10 mA cm-2), and smallest Tafel slope (90 mV dec-1) value. Furthermore, the OH˙ radicals produced during the OER electrochemically degraded the MB to 90% within 2 hours. The stability test conducted at 20 mA cm-2 showed almost negligible loss of the electrochemical response for OER, with 99% retention of the original response. These results strongly suggest that this catalyst is a promising candidate for addressing the challenges of wastewater treatment and energy generation.

Bifunctional electrochemical OER and HER activity of Ta2O5 nanoparticles over Fe2O3 nanoparticles

We have synthesized a Fe2O3/Ta2O5 double oxide heterostructure using a facile hydrothermal method. The resulting composite exhibits strong OER/HER activity - at an overpotential of 231/201 -and a Tafel slope value of 80/136 mV dec−1 in an alkaline and acidic medium respectively.

Multifunctional Ni3S2@NF-based electrocatalysts for efficient and durable electrocatalytic water splitting.

Transition-metal sulfides (TMSs) have indeed drawn dramatic interest as a potential species of electrocatalysts by virtue of their unique structural features. However, their poor stability and inherent activity have impeded their use in electrocatalytic water splitting. Here, we provide a rational design of a hierarchical nanostructured electrocatalyst containing CeOx-decorated NiCo-layered double hydroxide (LDH) coupled with Ni3S2 protrusions formed on a Ni foam (NF). Specifically, the as-prepared electrocatalyst, denoted as Ni2Co1 LDH-CeOx/Ni3S2@NF, presents only 250 and 300 mV overpotential at ±100 mA cm-2, respectively, along with the Tafel slope values of 92 and 52 mV dec-1, as well remarkable long-term life for water splitting in an alkaline electrolyte. Based on systematic experiments and theoretical analysis, the superior electrocatalytic property in terms of Ni2Co1 LDH-CeOx/Ni3S2@NF can be imputed to the following reasons: the porous framework of Ni3S2@NF provides a largely surface area and high conductivity; the NiCo LDH nanosheets provide enriched active sites and favorable adsorption ability; the oxygen-vacancy-rich CeOx optimizes the electronic configuration. Overall, these factors work synergistically to expedite the catalytic kinetics of splitting water. Our work concentrates on a rational interface to devise efficient, multifunctional, and serviceable electrocatalysts for future applications.

Development of robust noble-metal free lanthanum, neodymium doped Li1.05Ni0.5Mn1.5O4 as a bifunctional electrocatalyst for electrochemical water splitting.

Catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are at the heart of water oxidation reactions. Despite continuous efforts, the development of OER/HER electrocatalysts with high activity at low cost remains a big challenge. Herein, we report a composite material consisting of Li1.05Ni0.5Mn1.5O4, Li1.05Ni0.5 La0.10Mn1.40O4, and Li1.05Ni0.5 Nd0.10Mn1.40O4 as a bifunctional electrocatalyst for OER and HER applications. Though the catalyst has a modest activity for HER, it exhibits high OER activity thereby making it a better nonprecious electrocatalyst for both OER and HER. The catalytic activity arises from the synergetic effects between LNM-La and LNM-Nd by a facile route that shows excellent and durable bifunctional catalytic activity for OER and HER in the alkaline medium developed. The LNM, LNM-La, and, LNM-Nd displayed current densities of 2.17 V, 1.68 V, and 1.93 V vs. RHE at 10 mA cm-2 respectively. The Tafel slope values obtained for LNM, LNM-La, and LNM-Nd are about 419 mV dec-1, 118 mV dec-1, and 378 mV dec-1 respectively. These results indicate the superior electrocatalytic activity of LNM-La with facile OER kinetics.

Mild construction of an Fe-B-O based flexible electrode toward highly efficient alkaline simulated seawater splitting

It is essential to construct self-supporting electrodes based on earth-abundant iron borides in a mild and economical manner for grid-scale hydrogen production. Herein, a series of highly efficient, flexible, robust, and scalable Fe-B-O@FeBx modified on hydrophilic cloth (denoted as Fe-B-O@FeBx/HC, 10 cm × 10 cm) are fabricated by mild electroless plating. The overpotentials and Tafel slope values for the hydrogen and oxygen evolution reactions are 59 mV and 57.62 mV dec−1 and 181 mV and 65.44 mV dec−1, respectively; only 1.462 V is required to achieve 10 mA cm−2 during overall water splitting (OWS). Fe-B-O@FeBx/HC maintains its high catalytic activity for more than 7 days at an industrial current density (400 mA cm−2), owing to the loosened popcorn-like Fe-B-O@FeBx that is firmly loaded on a 2D-layered and mechanically robust substrate along with its fast charge and mass transfer kinetics. The chimney effect of core–shell borides@(oxyhydro)oxides enhances the OWS performance and protects the inner metal borides from further corrosion. Moreover, the flexible Fe-B-O@FeBx/HC electrode has a low cost for grid-scale hydrogen production ($2.97 kg−1). The proposed strategy lays a solid foundation for universal preparation, large-scale hydrogen production and practical applications thereof.

Alloying Pt into Ni partially amorphous for promoted alkaline hydrogen production

Aiming at the sluggish water dissociation step in alkaline hydrogen evolution reaction (HER), the platinum-nickel alloy material (PtNi10/C) featuring unique crystalline/amorphous structure supported on carbon black is deliberately designed and fabricated via a reversely rapid co-precipitation and mild thermal reduction strategy. Electrochemical results show that only 66 mV of overpotential is needed for PtNi10/C to drive a current density of 10 mA cm−2 at a lower platinum loading (8.3 μgPt cm-2 geo), which is much lower than that of other catalysts with a single metal source(S-Ni/C and S-Pt/C) and even the commercial Pt/C catalyst (20 wt%). The target catalyst also exhibits smaller tafel slope value (16.73 mV dec−1) and electrochemical impedance value, enabling a fast kinetics rate for water dissociation. Partial crystallization facilitates moderate adsorption of intermediates, while the high-valence Ni(II) and Pt(II) species serve as pivotal driving force for the kinetic dissociation of water. The unique microstructure of PtNi10/C shows a remarkable advantage toward HER in alkaline but acidic medium. In addition, other transition metal-based catalysts following the similar protocol are also fabricated and present varying degrees of HER performance. Hence, the facile and rapid co-precipitation/thermal reduction strategy proposed in this study provides some guidelines for designing high-efficiency alkaline HER catalysts.

Poly(amidoamine) dendrimer-protected Pt nanoparticles as a catalyst with ultra-low Pt loading for PEM water electrolysis

Carbon-supported Pt-based electrocatalysts have been widely used on the cathode in proton-exchange membrane water electrolyser (PEM WE) for efficient H2 production. Graphitized carbon supports provide high electrical conductivity to catalyst layer and immobilize Pt nanoparticles (NPs), delivering high current densities (1 to 3 A cm−2) with durability during operation under acidic environment. However, use of Pt loadings as high as ∼20 and ∼40 wt.% in carbon support are detrimental for large-scale H2 production. In this work, PEM water electrolysis was performed using a single-cell assembly, constructed using carbon-supported dendrimer-encapsulated Pt nanoparticles (Dend-PtNPs) as the cathode and Ir black as the anode. Main aim of this study was to prepare/encapsulate Pt NPs within the dendrimer (Dend) with different surface groups (COONa, -NH2, -OH) and various generations (G3-G6). This was done in order to target ultralow Pt loadings (1 to 2 wt% on carbon) and anchor the resulting Dend-PtNPs onto highly conductive multi-layered graphene (MLG) support using 1-ethyl-3-(3-dimethylamino propyl) carbodiimide (EDC) and N‑hydroxyl sulfoxuccinimide (NHS) as the cross-linking agents for efficient H2 evolution reaction (HER). The amount of cross-linking agents used for the synthesis of Dend-PtNPs were optimised to achieve optimal HER performance. The mass loading of Pt on MLG support was determined using ICP-OES spectrometry. The MLG/Dend-PtNPs prepared by carboxylate (COONa) surface groups showed the excellent HER performance at zero potential and smaller Tafel slope value of 35 mV dec−1. The PEM WE performance of commercial catalyst (40% Pt on C) was compared with as prepared MLG/Dend-PtNPs catalyst with 1 to 2 wt.% Pt loading.

Gold nanoparticles decorated covalent organic polymer as a bimodal catalyst for total water splitting and nitro compound reduction

The design and construction of a bimodal catalyst with magnificent performance and high stability is a debatable one for total water splitting and nitro compound reduction. Herein, we report the synthesis of a covalent organic polymer network based on 1,4-phenylenediamine based covalent organic polymer (PD-COP) and its decoration with Au nanoparticles (Au NPs) as well as their confirmation using various analytical and surface techniques. The electrocatalytic activity toward total water-splitting reaction (OER and HER) in KOH solution (1.0 M) was investigated. In addition, the reduction of aromatic nitro compounds (4-nitrophenol (4-NP) and 2-nitroaniline (2-NA)) was carried out in the presence of NaBH4. Among the different electrocatalysts (PD-COP, Au@PD-COP-I, Au@PD-COP-II, Au@PD-COP-III and Au@PD-COP-IV) studied in this work, the Au@PD-COP-II demands a low overpotential of 288 mV and 184 mV to attain a 50-mA/cm2 geometrical current density with a lowest Tafel slope value of 56 and 85 mV/dec for OER and HER respectively. From the OER and HER phenomenal activity, a two-electrode system was constructed, and it needs a cell voltage of 1.615 V to conquer a current density of 10 mA/cm2 with outstanding stability for 34 h. The high electroactivity of Au@PD-COP-II may be allied with the presence of innumerable redox-active sites and high electrochemical active surface area (ECSA) towards effective water electrolysis. Further, the catalytic activity performed towards the reduction of 4-NP to 4-aminophenol (4-AP) and 2-NA to o-PDA (o-phenylenediamine), Au@PD-COP-II showed good catalytic activity with a reduction time of 20 and 14 min respectively.

Modulating the Surface Electronic Structure of Active Ni Sites by Engineering Hierarchical NiFe-LDH/CuS over Cu Foam as an Efficient Electrocatalyst for Water Splitting.

Water electrolysis encounters a challenging problem in designing a highly efficient, long durable, non-noble metal-free electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Here, in our work, a two-step hydrothermal reaction was performed to construct a hierarchal NiFe-layer double hydroxide (LDH)/CuS over copper foam for the overall water splitting reaction. While employed the same as an anode material, the designed heterostructure electrode NiFe-LDH/CuS/Cu exhibits excellent OER performance and it demands 249 mV overpotential to reach a current density of 50 mA cm-2 with a lower Tafel slope value of 81.84 mV dec-1. While as a cathode material, the NiFe-LDH/CuS/Cu shows superior HER performance and it demands just 28 mV of overpotential value to reach a current density of 10 mA cm-2 and a lower Tafel slope value of 95.98 mV dec-1. Hence, the NiFe-LDH/CuS/Cu outperforms the commercial Pt/C and RuO2 in terms of activity in HER and OER, respectively. Moreover, when serving as both the cathode and anode catalysts in an electrolyzer for total water splitting, the synthesized electrode only needs a cell potential of 1.55 V versus RHE to reach a current density of 20 mA cm-2 and long-term durability for 25 h in alkaline media. To study the interfacial electron transfer, Mott-Schottky experiments were performed, representing that the electron is transferred from n-type NiFe-LDH to p-type CuS as a result of creating the p-n junction in NiFe-LDH/CuS/Cu. The formation of this p-n junction allows the LDH layer to be more active toward the OH- adsorption and thereby could allow the OER or HER with a less energy input. This work affords another route to a cost effective, highly efficient catalyst toward producing clean energy across the globe.

Impact of Ligand in Bimetallic Co, Ni-Metal-Organic Framework towards Oxygen Evolution Reaction

Emerging materials based on metal-organic frameworks (MOFs) have the potential to be used in electrocatalytic energy storage applications. Nevertheless, a large-scale feasible useage of MOFs is hampered by the low conductivity and masking of the active metal centre by the organic linker. In this study, a NiCo-based benzene tricarboxylic (BTC) electrocatalyst was successfully synthesized, and the properties were fine-tuned with 4,4′-bipyridine as a second ligand which benefits the charge transfer kinetics through non-covalent π–π interaction. This approach yields an exceptional performance towards oxygen evolution reaction (OER) at three different KOH concentrations 1, 0.5, and 0.1 M. The electrocatalyst NiCo-Bpy-BTC when tested under three different concentrations of KOH, exhibited overpotentials of 292, 343, and 407 mV to reach the 10mA cm−2 current density respectively. The obtained Tafel slope values were lower than those of Ni-Bpy-BTC, Co-Bpy-BTC, and bare NiCo-BTC respectively. Moreover, we have achieved long-term durability for up to 16 h in all KOH concentrations. Our strategy interconnects reticular chemistry and materials electrochemistry and this new approach is useful in the design of new materials for energy-related applications.

Electrochemical Investigation of the OER Activity for Nickel Phosphite-Based Compositions and Its Morphology-Dependent Fluorescence Properties

Herein, we present the investigation of catalytical and fluorescence properties for Ni11(HPO3)8(OH)6 materials obtained through a hydrothermal approach. As part of the constant search for new materials that are both cost effective and electrocatalytically active for the oxygen evolution reaction (OER) in alkaline medium, the present study involves several graphite electrodes modified with Ni11(HPO3)8(OH)6 mixed with reduced graphene oxide (rGO) and carbon black. The experimental results obtained in 0.1 mol L–1 KOH electrolyte solution show the electrode modified with rGO, 5 mg carbon black and 1 mg nickel phosphite as displaying the highest current density. This performance can be attributed to the synergistic effect between nickel phosphite and the carbon materials. Investigation of the electrode’s OER performance in 0.1 mol L–1 KOH solution revealed a Tafel slope value of just 46 mV dec–1. By increasing the concentration to 0.5 and 1 mol L–1, this value increased as well, but there was a significant decrease in overpotential. Fluorescence properties were analyzed for the first time at the excitation length of 344 nm, and the observed strong and multiple emissions are described.

Electrosynthesis of Low Pt‐Loaded High Entropy Catalysts for Effective Hydrogen Evolution with Improved Acidic Durability

The synergistic effect in multi‐metal electrocatalysts has gained attention as an efficient strategy for enhancing intrinsic electrocatalytic activities. In this study, a facile electrodeposition technique is used to synthesize a multi‐metal high entropy catalyst (HEC) for efficient electrocatalytic hydrogen production. To boost the synergistic effect between noble metals and transition metals, the Pt ratio is controlled in a multi‐metal electrocatalyst system. The prepared Pt‐involved HEC (Pt‐HEC) exhibits a bamboo‐like morphology with uniformly distributed elements. The 2.5 mM Pt‐HEC has outstanding electrocatalytic activity toward hydrogen evolution reaction (HER) among other Pt‐HECs, with a low overpotential of 70 mV and a Tafel slope value of 47 mV dec−1. Additionally, the Pt mass activity of the 2.5 mM Pt‐HEC is 5.6 times higher than commercial Pt/C electrocatalyst owing to the improved synergistic effect with an optimized Pt ratio. According to the electrochemical impedance spectroscopy (EIS) analysis, the proton‐coupled electron transfer (PCET) process occurs more quickly in the 2.5 mM Pt‐HEC electrocatalyst, confirming its smaller charge transfer resistance properties compared to those of the 5 and 1 mM Pt‐HEC. Therefore, HEC systems can be extensively encouraged as a platform for improving synergistic effects and enhancing electrocatalytic activities for a highly efficient HER electrocatalyst.

3D nanosheet networks like mesoporous structure of NiO/CoSe2nanohybrid directly grown on nickel foam for oxygen evolution process

The advancement of energy conversion and storage frameworks depends significantly on the development of reliable, effective, and affordable electrocatalysts. Steadily, there is an increasing demand of energy, fossil fuels consumption, and alarming environmental issues that have induced researchers to find alternate renewable sources. For this purpose, water splitting using various electrocatalysts have been investigated in a highly favourable virtual environment and is a highly demanding challenge to fulfil the energy crises. Here in this work, we fabricated three-dimensional (3D) nanosheet network NiO/CoSe2/NF nanocomposite (where NF represents nickel foam) material via hydrothermal treatment. All the synthesized materials like NiO/NF, CoSe2/NF, and NiO/CoSe2/NF nanohybrid are tested for the oxygen evolution process in a basic medium (1.0M KOH). Among all directly grown NiO/CoSe2 3D nanosheet has shown the lowest overpotential (263 mV), Tafel slope value (38 mVdec−1), which is remarkably improved as compared to the pristine NiO/NF and CoSe2. The resultant enhanced performance is due to improved morphological characteristics, increased surface area, and electrochemical coupling of electrons between NiO/NF and CoSe2/NF due to the synergistic effect.

Single-Source-Precursor Derived Transition Metal Alloys Embedded in Nitrogen-Doped Porous Carbons as Efficient Oxygen Evolution Electrocatalysts.

Carbon supported metallic nanomaterials are of great interest due to their low-cost, high durability and promising functional performance. Herein, a highly active oxygen evolution reaction (OER) electrocatalyst comprised of defective carbon shell encapsulated metal (Fe, Co, Ni) nanoparticles and their alloys supported on in-situ formed N-doped graphene/carbon nanotube hybrid is synthesized from novel single-source-precursors (SSP). The precursors are synthesized by a facile one-pot reaction of tannic acid with polyethylenimine and different metal ions and subsequent pyrolysis of the SSP. Benefiting from the heteroatom doping of carbon and formation of well-encapsulated metal/alloy nanoparticles, the obtained FeNi@NC-900 catalyst possesses lowest overpotentials of 310 mV to achieve a current density of 10 mA cm-2 for OER with a small Tafel slope value of 45 mV dec-1 , indicating excellent catalytic performance due to the following features: (1) A synergistic electronic effect among metal alloy nanoparticles, nitrogen-doped carbon, and entangled carbon nanotubes; (2) penetration of electrolyte is promoted towards the active sites through the porous structure of the formed mesoporous carbon clusters; (3) the unique core-shell nanostructure of the hybrid material effectively curbs the degradation of electrocatalyst by protecting the alloy nanoparticles from harsh electrolyte. This work advances an inexpensive and facile method towards the development of transition metal-based hybrid material for potential energy storage and conversion.