Ni Foam Research Articles

Pd-substitution impact in nickel–cobalt spinel oxide grown on Ni foam as very effectual electrocatalyst for green hydrogen production supported by DFT study

The hydrothermal preparation of catalytic NiPdxCo2-xO4 (x ≦ 0.08) nano-electrocatalysts on Ni foam (NF) was successfully accomplished. The morphology and chemical composition of the catalysts are confirmed by advanced analytical techniques XRD, SEM, EDX, TEM, HR-TEM, and XPS. The NiPdxCo2-xO4 (x = 0.06) NF nano-electrocatalyst demonstrated remarkable performance in the HER, with an overpotential of 191.6 mV, a Tafel slope of 84.7 mV/dec, and extraordinary stability over 24 h using chronopotentiometry methods. The surface and electrochemical analyses demonstrated that the sample, doping with a 6.0% Pd2+ concentration, had appreciably enhanced performance in the HER. The improvement may be attributed to a much larger electrochemical surface area and fast charge transfer kinetics at the semiconductor and electrolyte interface. The influence of Pd dopants on the HER performance of CNs is studied with the help of density functional theory. It elucidates the way in which hydrogen and water molecules bind to the surface of PCN slabs. The theoretical results suggest that the incorporation of Pd dopants enhances the electrocatalytic process and boosts the HER activity as the concentration of Pd increases. The density of state spectra reveals their effect on spin-dependent electronic structure characteristics. Our findings point to a practical path for creating distinctive electrocatalysts that will serve as better electrodes for a variety of forthcoming hydrogen fuel cell applications.

Aqueous alternating electrolysis prolongs electrode lifespans under harsh operation conditions

It is vital to explore effective ways for prolonging electrode lifespans under harsh electrolysis conditions, such as high current densities, acid environment, and impure water source. Here we report alternating electrolysis approaches that realize promptly and regularly repair/maintenance and concurrent bubble evolution. Electrode lifespans are improved by co-action of Fe group elemental ions and alkali metal cations, especially a unique Co2+-Na+ combo. A commercial Ni foam sustains ampere-level current densities alternatingly during continuous electrolysis for 93.8 h in an acidic solution, whereas such a Ni foam is completely dissolved in ~2 h for conventional electrolysis conditions. The work not only explores an alternating electrolysis-based system, alkali metal cation-based catalytic systems, and alkali metal cation-based electrodeposition techniques, and beyond, but demonstrates the possibility of prolonged electrolysis by repeated deposition-dissolution processes. With enough adjustable experimental variables, the upper improvement limit in the electrode lifespan would be high.

Spatially engineered local electric field for enhanced water electrolysis

Alkaline water electrolysis (AWE) stands as a well-established and promising route for sustainable hydrogen production. However, traditional AWE cells suffer from low performance and bulky size. Here, we introduce the integrated design, a streamlined architecture that maximizes space utilization and enhances inter-component contact. This geometric innovation requires only minor modifications in the manufacturing process to effectively double the gas production capacity without increasing the volume of the device across a wide voltage range. Utilizing Ni foam electrodes, the device achieves a 205 mA cm−3 output at 2.0 V. Through visual inspections and simulations, we compared the new and traditional designs, attributing performance improvements to optimized local electric fields. These findings not only demonstrate the feasibility of spatial engineering, but also illuminate a promising path to advance alkaline water electrolyzer technology.

Hydrogen generation from catalytic hydrolysis of ammonia borane with Co-Cu-B/g-C3N4/NF catalyst

In this study, different double-supported Co-Cu-B/g-C3N4/Ni foam (NF=Ni foam) catalysts were synthesized by chemical deposition method in a certain pH value range (pH value between 10.5 and 12.0). Their catalytic performances of hydrolyzing ammonia borane (NH3BH3) hydrolysis were investigated to produce hydrogen at 298 K. Because of the adding of g-C3N4 in the plating solution, the obtained sample had certain photocatalytic activity when the visible light was introduced the hydrolysis experiment. The results displayed that the as-prepared Co-Cu-B/g-C3N4/NF catalyst at pH = 10.5 exhibited an improved catalytic effect for NH3BH3 hydrolysis under visible light irradiation. The corresponding hydrogen generation rate reached 8893 mol·min−1·g−1, and the activation energy was 41.8 kJ·mol−1. The catalytic performance of Co-Cu-B/g-C3N4/NF catalysts prepared by this method is better than that of as-obtained mono-metal Co-B/g-C3N4/NF catalyst. More importantly, its activity has exceeded many single-carrier cobalt-based catalysts reported so far, and even some single-support precious metal catalysts for NH3BH3 hydrolysis. It indicated that the strategy of double carriers and introduction of light contributed to the improvement in catalytic activity for the non-noble metal-based catalysts during NH3BH3 hydrolysis.

Anchoring magic NiCo2O4/NiO on Ni foam as an effective and binder-free electrocatalyst for boosting hydrogen evolution reaction

Electrocatalysts that can sustain water splitting without corrosion are required for large-scale water electrolysis applications. Thus, designing and constructing stable electrocatalysts is known as a crucial role in hydrogen evolution reactions (HER). Herein, NiCo2O4/NiO nanocubes on Ni foam (NF) as a stable electrocatalyst were fabricated successfully by using a facile hydrothermal method. Field Emission Scanning Electron Microscopy (FESEM) confirms the formation of distinct magic NiCo2O4/NiO/NF nanocubes with a size of 50–150 nm. The electrochemical tests indicated that the NiCo2O4/NiO nanocubes possess long stability of about 140 h and exceptional HER activity with a low overpotential of 38 mV at a current density of 10 mA.cm−2 in a 1 M potassium hydroxide (KOH) and a Tafel slope of only 45 mV.dec−1. The obtained results indicated that this level of HER catalytic performance is assigned to the rough surface and synergistic interactions between Ni and Co atoms in the nanocubes. It was also determined that the existence of NiO interface layer causes robust adhesion between NF and NiCo2O4 nanocubes. In addition, this discovery points to an advantageous future for the configuration and synthesis of highly effective, non-precious metal-based electrocatalysts for large-scale hydrogen production via water-splitting.

Self-supported copper/copper oxide microspheres for efficient electrocatalytic removal of low-concentration nitrate from aqueous solutions

The electrochemical removal of nitrate (NO3−) from aqueous solutions is a promising strategy for wastewater treatment; however, highly active catalysts are required. In this study, self-supported Cu/copper oxide (CuO) microspheres (ms) on Ni foam (NF) (Cu/CuOms/NF) were fabricated for NO3− removal from water using an electrochemical method, achieving a transformation efficiency of up to 99.72 % and N2 selectivity of 97.97 %. Cu/CuOms/NF also exhibited excellent NO3− removal performance over a wide pH range, while maintaining extremely low levels of toxic ammonia residues. The Cu/CuOms/NF-driven NO3− removal rate remains as high as 95.45 % even after recycling for five times, demonstrating the remarkable electrochemical stability of the catalyst. The Cu/CuOms supported on NF provided active sites and accelerated the oxidation cycle involving Cl−, leading to the complete transformation of NO3− into harmless N2 gas. Therefore, this study not only achieved the environmentally friendly treatment of NO3− pollutants in wastewater but also provided a promising strategy for developing catalysts for electrochemical NO3− removal.

In Situ Formation of an Artificial Lithium Oxalate-Rich Solid Electrolyte Interphase on 3D Ni Host for Highly Stable Lithium Metal Batteries.

Li metal, with a high theoretical capacity, is considered the most promising anode for next-generation high-energy-density batteries. However, the commercialization of the Li metal anode is limited owing to its high reactivity, significant volume expansion, continuous solid electrolyte interphase (SEI) layer degradation caused by undesirable Li deposition, and uncontrollable dendrite growth. This study demonstrates the in situ construction of a Li2C2O4-enriched SEI layer from NiC2O4 nanowires on three-dimensional Ni foam. The lithiophilic Li2C2O4-enriched SEI layer provides a uniform distribution of the electrical field and sufficient nucleation and deposition sites for Li without dendrite formation. Consequently, the stable Li2C2O4-enriched SEI layer successfully inhibits the formation of lithium dendrites, resulting in reversible Li stripping/plating behavior, maintained over an extended period of 5000 h with a deposition capacity of 1 mAh cm-2 at 1 mA cm-2. Additionally, a high cycling stability is observed in the full cell test with ∼70% capacity retention after 1300 cycles at 3 C. This approach offers a large-scale and facile synthesis process via the in situ precipitation growth of NiC2O4 followed by lithiation to form Li2C2O4. Furthermore, the significant stability of the Li2C2O4-enriched SEI layer aids the design of in situ-constructed SEI layers for highly stable Li metal batteries.

Trace Pt-loading transition metal hydroxides as efficient catalyst for vaporized hydrogen peroxide decomposition

Vaporized hydrogen peroxide (VHP) holds great promise for the decontamination of space environment. Nevertheless, following the decontamination process, highly concentrated VHP within confined spaces is harmful to the human body. Hence, trace Pt-loading (0.57 wt%) transition metal hydroxides nanosheets anchored on Ni foam (Pt@NiAlCrFe-LDHs/NF) were prepared for VHP decomposition. Importantly, a strong electronic interaction between NiAlCrFe layer double hydroxides (NiAlCrFe-LDHs) and Pt was evidenced by XPS. Meanwhile, unique nanosheet-like morphology and rich mesoporous structure endow the catalyst with excellent performance. The catalytic activity of Pt@NiAlCrFe-LDHs/NF is approximately twice that of NiAlCrFe-LDHs/NF and seven times that of Pt/NF. The improved catalytic efficiency of Pt@NiAlCrFe-LDHs/NF results from the reduction in energy barrier for VHP decomposition reaction caused by the introduction of trace Pt. After ten recycling experiments, this catalyst still shows good durability with no significant deterioration in VHP decomposition efficiency. Finally, the growth mechanism of Pt@NiAlCrFe-LDHs/NF was also proposed and discussed.

Flameless venting characteristics and design model of micro-nano PMMA dust explosion

The effects of Fe–Ni foam thickness and dust size on flame propagation, reduced overpressure, and venting efficiency in 30 μm and 150 nm polymethyl methacrylate (PMMA) dust explosions were investigated. The flame quenching mechanism was revealed by coupling the heat transfer and flow of the dust flame within the Fe–Ni foam. It is found that micron dust is more prone to quenching than nano dust, and the differences in the quenching process of micro-nano dust are explained by combining the dust combustion kinetics and the theory of inter-particle heat transfer. The pressure venting mechanism of micro-nano dust was analysed under different thicknesses of Fe–Ni foam, and the thermal expansion effect of the flame passing through the Fe–Ni foam and its flow resistance significantly increased the reduced explosion overpressure. The flow continuity of the micro-nano dust was classified by means of the Knudsen number (Kn), which elucidates the effect of dust size differences on the pressure evolution. A prediction model for the maximum reduced explosion overpressure is proposed based on the explosion pressure venting of micro-nano dust. Changes in vented pressure have a direct impact on the efficiency of flameless venting. Nano-dust has an efficiency of more than 20 % lower than that of micron dust.

Electrocatalytic Valorization of Nitrate and Polyester Plastic for Simultaneous Production of Ammonia and Glycolic Acid.

Electrochemical upcycling of nitrate and polyester plastic into valuable products is an ideal solution to realize the resource utilization. Here, the co-production of ammonia (NH3) and glycolic acid (GA) via electrochemical upcycling of nitrate and polyethylene terephthalate (PET) plastics over mesoporous Pd3Au film on Ni foam (mPd3Au/NF), which is synthesized by micelle-assisted replacement method, is proposed. The mPd3Au/NF with well-developed mesoporous structure provides abundant active sites and facilitated transfer channels and strong electronic effect. As such, the mPd3Au/NF exhibits high Faraday efficiencies of 97.28% and 95.32% at 0.9V for the formation of NH3 and GA, respectively. Theoretical results indicate that the synergistic effect of Pd and Au can optimize adsorption energy of key intermediates *NOH and *OCH2-CH2OH on active sites and increase bond energy of C─C band, thereby improving the activity and selectivity for the formation of NH3 and GA. This work proposes a promising strategy for the simultaneous conversation of nitrate and PET plastic into high-value NH3 and GA.

Rational Construction of a 3D Self-Supported Electrode Based on ZIF-67 and Amorphous NiCoP for an Enhanced Oxygen Evolution Reaction.

The development of efficient and Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is an urgent requirement in the field of electrochemical water splitting. The electrocatalytic performance of the OER can be greatly enhanced by the synergistic combination of zeolite imidazolate frameworks (ZIFs) and transition-metal phosphides, both of which individually exhibit promising capabilities in this regard. In this study, a novel amorphous NiCoP deposited on ZIF-67 sheets supported on Ni foam (labeled as NiCoP/ZIF-67/NF) as an OER electrocatalytic material was successfully synthesized using a simple, secure, and time-efficient two-step strategy. The experimental results demonstrate that NiCoP/ZIF-67/NF possesses a large active surface area with abundant active sites. Also, the synergistic effect and interaction between NiCoP and ZIF-67, as well as between Ni and Co within NiCoP, effectively enhance its electrochemical performance under alkaline conditions. Consequently, NiCoP/ZIF-67/NF exhibits outstanding catalytic activity for OER with an overpotential (η) of 175 mV at a current density of 10 mA cm-2 and a long-term stability over 40 h at 20 mA cm-2 in a 1.0 M KOH electrolyte. The corresponding analyses suggest that the real active sites responsible for the OER are identified as NiOOH and CoOOH species within the structure of NiCoP/ZIF-67/NF. Additionally, the catalytic function and stability of ZIF-67 toward the OER under alkaline conditions were also briefly discussed. This work provides a novel catalytic material for the OER along with a facile strategy to fabricate superior, efficient, and noble metal-free catalysts suitable for energy-related applications.

Taking Advantage of Potential Coincidence Region: Insights into Gas Production Behavior in Advanced Self-Activated Hydrazine-Assisted Alkaline Seawater Electrolysis.

Water electrolysis assisted by hydrazine has emerged as a prospective energy conversion method for achieving efficient hydrogen generation. Due to the potential coincidence region (PCR) between the hydrogen evolution reaction (HER) and the electro-oxidation of hydrazine, the hydrazine oxidation reaction (HzOR) offers distinct advantages in terms of strategy amalgamation, device architecture, and the broadening of application horizons. Herein, we report a bifunctional electrocatalyst of interfacial heterogeneous Fe2P/Co2P microspheres supported on Ni foam (FeCoP/NF). Benefiting from the strong interfacial coupling effect between Fe2P and Co2P and the three-dimensional microsphere structure, FeCoP/NF exhibits outstanding bifunctional electrocatalytic performance, achieving 10 mA cm-2 with low overpotentials of 10 and 203 mV for HER and HzOR, respectively. Utilizing FeCoP/NF for both electrodes in HzOR-assisted water electrolysis results in significantly reduced potentials of 820 mV for 1 A cm-2 in contrast to the electro-oxidation of alternative chemical substrates. The presence of a potential coincidence region makes the application of self-activated seawater electrolysis realistic. The gas production behavior at different current densities in this interesting hydrogen production system is discussed, and some rules that are distinguished from conventional water electrolysis are summarized. Furthermore, a new self-powered hydrogen production system with a direct hydrazine fuel cell, rechargeable Zn-hydrazine battery, and hydrazine-assisted seawater electrolysis is proposed, emphasizing the distinct benefits of HzOR and its potential role in electrochemical energy conversion technologies powered by renewable sources.

In-situ growth of novel iron oxide/iron organic framework composites as efficient electroactive materials of battery supercapacitor hybrids

Iron oxide (Fe2O3) with a high theoretical capacitance, wide potential ranges and easy availability has attracted much attentions as the electrode material of battery supercapacitor hybrids (BSH). Metal–organic framework (MOF) is one of the promising potential energy storage materials due to its large surface area and controllable pore structures. In this work, novel iron oxide/iron organic framework composites (Fe2O3/FeMOF) are in-situ grown on the Ni foam as efficient energy storage electrodes of BSH. By tuning the solvothermal durations, the morphology changes from random sizes of sheets, regular grown vertical sheets, to flower-like structures. The d-spacing also increases for the Fe2O3/FeMOF synthesized using longer solvothermal durations. The optimal Fe2O3/FeMOF electrode synthesized using 9 h shows a high areal capacitance of 10.97 F/cm2 along with an areal capacity of 5.49 F/cm2 at the current density of 35 mA/cm2, owing to the most regular growth of sheets, the large d-spacing, and the smallest charge-transfer resistances. A BSH composed of the Fe2O3/FeMOF positive electrode and a graphene negative electrode shows a maximum energy density of 0.76 mWh/cm2 at 22.5 mW/cm2. The excellent long-term cycling stability with the capacitance retention of 85% and Coulombic efficiency of 98% are also achieved after 10,000 charge/discharge cycles.

Enhancement of urea oxidation reaction in alkaline condition via heterointerface engineering

Water electrolysis involving low energy barrier anodic urea oxidation reaction (UOR) is a promising way for hydrogen production. In this study, we present a superior heterostructured UOR electrocatalyst of (NiFeCo)Sx/FeOOH/NiFeCo(OH)x supported on conductive Ni foam prepared using a simple, ultrafast, energy-saving single-step corrosion engineering method. Leveraging the high conductivity of the (NiFeCo)Sx, plentiful Fe3+ in the amorphous FeOOH, high catalytic activity of the NiFeCo(OH)x, and abundant heterointerfaces, the resulting (NiFeCo)Sx/FeOOH/NiFeCo(OH)x electrode exhibits remarkable electrocatalytic performance toward UOR under alkaline condition. The electrocatalyst shows an ultra-low potential of 1.36 V at 100 mA cm−2, a small Tafel slope of 24.8 mV dec–1, and excellent stability. Density functional theory calculation shows that the multiple heterointerfaces provide synergistic effect of shifting the d-band center to optimize the intermediate chemisorption energy, thus boosting the catalytic kinetics for catalyzing UOR.

Two infrequent organic hybrid transition metal hexa-sulfide electro-catalysts for the efficient oxygen evolution reaction

The exploration of the cheap oxygen evolution reaction (OER) electro-catalysts together with high efficient activity is highly imperative for obtaining clean and renewable hydrogen energy. Herein, two novel organic hybrid transition metal hexa-sulfide electro-catalysts [TM(S6)(tptz)] [TM = Zn (1) and Mn (2), tptz = 2,4,6-tris-2-pyridyl-1,3,5-triazine] with rare poly-sulfur S62- anion was isolated from the facile solvothermal reaction of sulfur powder, transition metal salt and tptz in anhydrous ethanol at 120 °C for 7 days. Both 1 and 2 are isostructural and show a distorted trigonal–pyramidal stereochemistry with chelate S62- anion and large π-conjugated aromatic tptz. 1 and 2 are used in combination with Ni nanoparticles and porous Ni foam (NF) to fabricate a 1/Ni/NF or 2/Ni/NF electrode as OER electro-catalyst, which delivers excellent OER activity with the low overpotential (233 mV for 1/Ni/NF and 241 mV for 2/Ni/NF at 10 mA·cm−2) and small Tafel slope (45.9 mV·dec-1 for 1/Ni/NF and 50.7 mV·dec-1 for 2/Ni/NF) in KOH alkaline electrolyte, and is evidently superior to the well-known OER electro-catalyst RuO2.

Inhibiting dissolution strategy achieving high-performance sodium titanium phosphate hybrid anode in seawater-based dual-ion battery

Aqueous sodium-ion batteries (ASIBs) show great promise as candidates for large-scale energy storage. However, the potential of ASIB is impeded by the limited availability of suitable anode types and the occurrence of dissolution side reactions linked to hydrogen evolution. In this study, we addressed these challenges by developing a Bi-coating modified anode based on a sodium titanium phosphate (NTP)-carbon fibers (CFs) hybrid electrode (NTP-CFs/Bi). The Bi-coating effectively mitigates the localized enrichment of hydroxyl anion (OH–) near the NTP surface, thus addressing the dissolution issue. Notably, the Bi-coating not only restricts the local abundance of OH– to inhibit dissolution but also ensures a higher capacity compared with other NTP-based anodes. Consequently, the NTP-CFs/Bi anode demonstrates an impressive specific capacity of 216.8 mAh/g at 0.2 mV/s and maintains a 90.7 % capacity retention after 1000 cycles at 6.3 A/g. This achievement sets a new capacity record among NTP-based anodes for sodium storage. Furthermore, when paired with a cathode composed of hydroxy nickel oxide directly grown on Ni foam, we assembled a seawater-based cell exhibiting high energy and power densities, surpassing the most recently reported ASIBs. This groundbreaking work lays the foundation for a potential method to develop long-life NTP-based anodes.

Zn2GeO4 rods/graphene supported on Ni foam as binder-free anode for enhanced Na ion storage performance

Zn2GeO4 rods/graphene supported on Ni foam as binder-free anode for enhanced Na ion storage performance

Electricity Generation by a Phototrophic Bacterium in a Glucose−Fed Double Chambered Microbial Fuel Cell Using a Fabricated 3D Anode Electrode

Study’s Novelty/Excerpt This study presents an approach to enhancing microbial fuel cell (MFC) performance by employing phototrophic bacteria (PTB) and sustainable electrode materials, specifically a 3D anode electrode fabricated from reduced graphene oxide (rGO) and nickel (Ni) foam. By integrating morphological, biochemical, and molecular techniques to identify the electrochemically active PTB, the research achieved a significant eight-fold increase in power density using rGO-Ni electrodes compared to conventional Ni electrodes. This work underscores the potential of utilizing sustainable materials and PTB to improve MFC efficiency and economic viability, offering a promising direction for sustainable bioelectricity generation. Full Abstract Over the past years, despite intensified research on microbial fuel cells (MFC), low power densities were recorded, reducing the productivity and economic viability of the process. This necessitated testing various MFC configurations, fabricating various electrodes, and evaluating various substrate types and species of electrogenic microorganisms to improve MFC performance. Despite the dual advantage of phototrophic bacteria (PTB), metabolizing organic waste substances and generating electricity, less research was conducted on the bacterium. Although a significant amount of energy is generated using unsustainable (fossil-based) materials in electrode fabrication, this study focuses on using sustainable materials like carbon cloth and graphite to fabricate a 3D anode electrode to exploit the maximum energy generated by PTB. The PTB used in this study was identified through morphological characteristics and biochemical tests (catalase and oxidase) and confirmed using a molecular technique: 16S rRNA sequencing. Preliminary results indicated that the PTB was gram-negative, spherical in shape, non−motile, and facultatively anaerobic bacterium. Analysis of the 16S rRNA partial sequence was conducted in GenBank databases. 100 significant sequences with the lowest and highest similarities of 84.10% and 98.76% were recorded, respectively. Of these, 13 strains had the highest similarities of >90%, all belonging to the genus Dysgonomonas, with D. oryzarvi Dy73 (98.76%) as the closest. Reduced graphene oxide (rGO) used as the anode was prepared using Hummer’s method by depositing the rGO on nickel (Ni) foam which changed the colour of Ni from grey to black after depositing and annealing. In addition to the SEM images, which showed a continuous multi−layered 3D scaffold on the Ni, the cyclic voltammetry (CV) analyses indicated an increase in the electrochemical activities of the rGO−Ni electrode compared to Ni. The CV also confirmed the bacterium to be electrochemically active. The 100 mL glucose−fed two−chamber MFC were separately run with the Ni and rGO–Ni as anode electrodes in a batch mode for 11 days, while carbon cloth was used as the cathode for both runs. An approximate 0.58 W/m2 power density was recorded for Ni, but eight−fold of Ni’s, 4.9 W/m2was generated by rGO−Ni. The study demonstrated that using fabricated 3D rGO–Ni as anode electrode can increase the microbial adhesion and power density of bacterium in MFC, thereby providing a more applicable and sustainable alternative to bioelectricity generation.

Hydrothermal synthesis of (NiFe/NiCo)S@NF bilayer electrocatalyst for efficient hydrogen evolution reaction

Hydrogen is widely recognized as a renewable and clean energy source that has the potential to reduce dependence on fossil fuels. However, it is crucial to develop efficient, affordable, and sustainable electrocatalysts for hydrogen production through water splitting. To tackle this challenge, a bilayer Ni–Fe–Co-based sulfide was hydrothermally grown on Ni foam to boost the hydrogen evolution reaction (HER). SEM images revealed the micro-sized NiFe sheets decorated with NiCo nanosheets on the surface. The (NiFe/NiCo)S@NF electrocatalyst demonstrated outstanding performance towards HER in a 1 M KOH solution, where only a low overpotential of 185 mV vs. RHE was required at −10 mA/cm2, being considerably lower than those for NiFeS@NF (230 mV), NiCoS@NF (229 mV), NiFe@NF (237 mV) and NiCo@NF (256 mV) electrodes. This improvement could be attributed to the synergistic effect between constituents, the presence of Ni3S2 and NiCo2S4 phases, and the higher exposed area provided by the 3D nano/micro structure of the (NiFe/NiCo)S@NF electrocatalyst. Furthermore, this electrocatalyst exhibited the lowest Tafel slope of 76 mV/dec compared to NiFeS@NF (92 mV/dec), NiCoS@NF (87 mV/dec), NiFe@NF (89 mV/dec), and NiCo@NF (102 mV/dec), indicating its faster HER kinetics. Finally, in a two-electrode system of (NiFe/NiCo)S@NF||(NiFe/NiCo)S@NF, a low voltage of 1.58 V was required to obtain a current density of 10 mA/cm2 and the synthesized electrocatalyst had excellent stability over 12 h electrolysis. The achieved results proved that the (NiFe/NiCo)S electrocatalyst has great potential as a highly efficient electrode material for alkaline HER.

Hierarchical nanoflowers of Bi/Fe-based selenide as a bifunctional electrocatalyst for alkaline water electrolysis

The current study presents a freestanding bifunctional electrocatalyst comprising hierarchically assembled Bi/Fe-based selenide with a nanoflower-like morphology on Ni foam for water electrolysis application. The impact of systematically adding Fe ions to Bi2Se3 on the phase and morphology is elaborately discussed. It is shown that tuning the Bi/Fe molar ratio governs the phase, electronic bandgap, and morphology, driven by the evolution of hetero-interfacial chemistry. The existence of multivalent metal ions, lattice defects, and an extended surface area remarkably improves the electrocatalytic activity. The optimized nanoflower-like composite electrode (1Bi1Fe-Se@NF) exhibits robust electrocatalytic efficacy with extremely low overpotentials of ∼53 mV and ∼230 mV at 10 mA cm−2 for hydrogen and oxygen evolution reactions, respectively. The symmetrical alkaline electrolyser, utilizing 1Bi1Fe-Se@NF electrodes (+,−), operates at a cell voltage of ∼1.52 V at 10 mA cm−2, lower than the device equipped with commercial Pt/C@NF (-) and RuO2@NF (+) (∼1.57 V). Even after 100 h of operation at 50 mA cm−2, the symmetrical cell maintains a stable voltage, highlighting the outstanding bifunctional catalytic activities of noble metal-free 1Bi1Fe-Se@NF for overall water electrolysis.