The great interest in rechargeable Zn–air batteries (ZABs) arouses extensive research on low‐cost, high‐active, and durable bifunctional electrocatalysts to boost the sluggish oxygen reduction ...reaction (ORR) and oxygen evolution reaction (OER). It remains a great challenge to simultaneously host high‐active and independent ORR and OER sites in a single catalyst. Herein a dual‐phasic carbon nanoarchitecture consisting of a single‐atom phase for the ORR and nanosized phase for the OER is proposed. Specifically, single Co atoms supported on carbon nanotubes (single‐atom phase) and nanosized Co encapsulated in zeolitic‐imidazole‐framework‐derived carbon polyhedron (nanosized phase) are integrated together via carbon nanotube bridges. The obtained dual‐phasic carbon catalyst shows a small overpotential difference of 0.74 V between OER potential at 10 mA cm−2 and ORR half‐wave potential. The ZAB based on the bifunctional catalyst demonstrates a large power density of 172 mW cm−2. Furthermore, it shows a small charge‐discharge potential gap of 0.51 V at 5 mA cm−2 and outstanding discharge‐charge cycling durability. This study provides a feasible design concept to achieve multifunctional catalysts and promotes the development of rechargeable ZABs.
A dual‐phasic carbon nanoarchitecture consisting of a single‐atom phase for oxygen reduction reaction (ORR) and nanosized phase for oxygen evolution reaction (OER) is proposed to boost the oxygen electrode performance for rechargeable Zn–air batteries, showing a small OER‐ORR overpotential difference (0.74 V), large power density (172 mW cm–2), a small charge‐discharge potential gap (0.51 V at 5 mA cm–2), and outstanding discharge‐charge cycling durability.
Development of easy‐to‐make, highly active, and stable bifunctional electrocatalysts for water splitting is important for future renewable energy systems. Three‐dimension (3D) porous Ni/Ni8P3 and ...Ni/Ni9S8 electrodes are prepared by sequential treatment of commercial Ni‐foam with acid activation, followed by phosphorization or sulfurization. The resultant materials can act as self‐supported bifunctional electrocatalytic electrodes for direct water splitting with excellent activity toward oxygen evolution reaction and hydrogen evolution reaction in alkaline media. Stable performance can be maintained for at least 24 h, illustrating their versatile and practical nature for clean energy generation. Furthermore, an advanced water electrolyzer through exploiting Ni/Ni8P3 as both anode and cathode is fabricated, which requires a cell voltage of 1.61 V to deliver a 10 mA cm−2 water splitting current density in 1.0 m KOH solution. This performance is significantly better than that of the noble metal benchmark—integrated Ni/IrO2 and Ni/Pt–C electrodes. Therefore, these bifunctional electrodes have significant potential for realistic large‐scale production of hydrogen as a replacement clean fuel to polluting and limited fossil‐fuels.
Three‐dimension nickel‐based electrocatalytic electrodes (Ni/Ni8P3 and Ni/Ni9S8) are developed for application in water splitting. The as‐obtained Ni/Ni8P3 catalytic electrode, particularly exhibiting excellent electrocatalytic activity and stability due to its advanced structure effects, can serve as a highly efficient and stable bifunctional catalyst for overall water splitting.
Display omitted
•MoS2/Fe2O3 heterostructure was fabricated by facile two-step electrodeposition.•Alteration in duration of the deposition steps regulated the water splitting efficiency.•Substrate ...adsorption–desorption and charge transfer efficiency of the heterostructure varied with deposition duration.•Tailored MoS2/Fe2O3 heterostructure outperformed water splitting activity of the state-of-the-art RuO2 || Pt/C electrolyzer.
Development of facile strategies to directly fabricate the noble-metal-free heterostructure on the conducting substrate and tailoring its electrocatalytic activity are crucial to achieve the superior overall water splitting activity. Herein, a series of MoS2/Fe2O3 heterostructure was directly fabricated on nickel foam substrate by a facile two-step electrodeposition technique. The alteration in duration of the deposition steps regulated the physicochemical properties and water splitting efficiency of the resulting heterostructure. A correlative investigation of Tafel and Nyquist plot revealed that the substrate adsorption–desorption and charge transfer efficiency of the heterostructure varied owing to this alteration. The successful integration of Fe2O3 with MoS2 synergistically enhanced the electrocatalytic activity of the heterostructure and binder-free growth on conducting nickel foam (NF) helped it to achieve higher catalytic current density. The heterostructure obtained through 5 and 6 min long two-step electrodepositions (F5M6), showed superior bifunctional electrocatalytic activity. The symmetric cell constructed with F5M6 electrode outperformed the state-of-the-art RuO2 || Pt/C electrolyzer at higher operating voltage region and was able to achieve a current density of 757 mA cm−2 at 2 V. Moreover, the heterostructure could sustain its overall water splitting proficiency for ~ 30 h at high current density confirming its excellent overall water splitting efficacy. This investigation established the two-step electrodeposition process as an effective electrocatalytic-activity-tailoring strategy.
Spinel oxide electrocatalysts supported on carbon nanofibers (CNFs), denoted as and NiMn2O4/CNF and NiCo2O4/CNF, are investigated for the oxygen evolution reaction (OER) in alkaline electrolyte. ...NiCo2O4/CNF and NiMn2O4/CNF are prepared according to an optimized electrospinning method using polyacrylonitrile (PAN) as carbon nanofibers precursor. After the thermal treatment at 900 °C for 1 h in the presence of helium and the subsequent one at 350 °C for 1 h in air, nanosized metal oxides with a spinel structure supported on carbon nanofibers are obtained. The physico-chemical investigation shows relevant difference in the crystallite size (9 nm for the NiCo2O4/CNF and 20 nm for the NiMn2O4/CNF) and a more homogeneous distribution for NiMn2O4 supported on carbon nanofibers. These characteristics derive from the different catalytic effects of Co and Mn during the thermal treatment as demonstrated by thermal analysis. The OER activity of NiCo2O4/CNF and NiMn2O4/CNF is studied in a single cell based on a zero gap anion-exchange membrane-electrode assembly (MEA). The NiMn2O4/CNF shows a better mass activity than NiCo2O4/CNF at 50 °C (116 A g−1 @ 1.5 V and 362 A g−1 @ 1.8 V vs. 39 A g−1 @ 1.5 V and 253 A g−1 @ 1.8 V) but lower current density at specific potentials. This is the consequence of a lower concentration of the active phase on the support resulting from the need to mitigate the particle growth in NiMn2O4/CNF.
•Metal oxide nanoparticles were synthesised through electrospinning.•Spinel structures supported on nanofibers were achieved after thermal treatment.•Lower load of NiMn2O4/CNF compared to NiCo2O4/CNF demonstrates better mass activity.
Electrochemical water splitting represents a viable route for hydrogen production, but its efficiency critically depends on developing effective electrocatalysts that minimize energy loss and ...material costs. This study introduces iridium-cobalt (Ir–Co) nanoparticles were synthesized on copper foam (CF) substrates using a one-step electrodeposition method. A comprehensive analysis was conducted on the morphology, chemical composition, and crystal structure of the electrocatalysts, along with a particular study on their electrocatalytic performance in the hydrogen evolution reaction (HER). The results demonstrate that high-index IrCo (311) crystal planes have been detected in the Ir–Co/CF electrocatalysts, which possess a tetradecahedral polycrystalline structure. The size of tetradecahedral nanoparticles is in the range of 180–250 nm. Ir–Co nanoparticles exhibit a balanced composition of approximately 49.8 at% Ir and 50.2 at% Co. The Ir–Co/CF electrocatalyst exhibits superior electrocatalytic activity in 1.0 M KOH solution, requiring only 46.8 mV overpotential to obtain a current density of 10 mA cm−2, with a low Tafel slope of 32.65 mV·dec−1. Additionally, the prolonged stability tests confirm the robustness of the Ir–Co/CF electrocatalyst, highlighting its potential for sustainable energy applications.
Display omitted
•Ir–Co tetradecahedral nanoparticles were synthesized with one-step electrodeposition.•Ir–Co alloy demonstrated polycrystalline structure with high-index (311) crystal planes.•Ir–Co electrocatalysts exhibited overpotential of 46.8 mV and low Tafel slope of 32 mV·dec−1.•Ir–Co electrocatalysts achieved exceptional stability during alkaline hydrogen evolution tests.
Hydrogen is a promising candidate for clean and sustainable energy resources to substitute fossil fuels to mitigate global environmental issues. Electrochemical hydrogen production has been regarded ...as a viable and promising strategy. The overall water splitting is currently the predominant electrochemical hydrogen production method, which could be driven by renewable energy to achieve sustainable production. However, the current challenges are the intrinsically sluggish and energy-intensive oxygen evolution reduction (OER) at the anode and the expensive noble metal-based catalysts for overall water splitting, which limit the practical applications. Extensive efforts have been made to develop bifunctional non-noble metal-based electrocatalysts to boost hydrogen production efficiency and lower the cost. Meanwhile, alternative oxidation reactions with faster kinetics and less energy requirement than OER are being explored as the anodic reaction to couple with the hydrogen evolution reaction for energy-saving hydrogen production. In this review, the non-noble metal-based bifunctional electrocatalysts for overall water splitting, as well as other novel energy-saving hydrogen productions have been introduced and summarized. Current challenges and outlooks are commented on at the end of the article.
Graphical abstract
The electrocatalysts with high activity and low cost are essential for hydrogen evolution reaction (HER). Herein, we report an approach to prepare hierarchical core-shell structures ZnxCo1-x/NC@MoS2. ...The Zn/Co ratio affects the particle sizes of ZnxCo1-x/NC polyhedra and the distribution of Co nanoparticles, resulting in the change of the amount of exposed active sites and further afforded tunable HER activities. Notably, the hybrids exhibit significantly superior catalytic activities to pristine MoS2. The optimal catalyst displays an extraordinary HER performance in acid media with a low overpotential of 130 mV at 10 mA cm−2 and high durability. The remarkable HER properties mainly originate from the fantastic structural characteristics such as abundant exposure of MoS2 edge-sites, uniform distribution of Co-Nx species, as well as the porousness and high conductivity of supports. This research provides a promising strategy to develop inexpensive and highly-efficient HER electrocatalysts derived from metal-organic frameworks and MoS2.
Display omitted
High-performance electrocatalysts with superior stability are critically important for their practical applications in hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). Herein, ...we report a facile method to fabricate urchin-like CoP nanocrystals (NCs) as catalyst for both HER and ORR with desirable electrocatalytic activities and long-term stability. The urchin-like CoP NCs with a diameter of 5 μm were successfully prepared by a hydrothermal reaction following a phosphidation treatment in N2 atmosphere and present excellent HER catalytic performance with a low onset overpotential of 50 mV, a small Tafel slope of 46 mV/decade, and an exceptional low overpotential of ∼180 mV at a current density of 100 mA cm–2 with a mass loading density of 0.28 mg/cm2. Meanwhile, a remarkable ORR catalytic activity was observed with a half-potential of 0.7 V and an onset potential of 0.8 V at 1600 rpm and a scan rate of 5 mV s–1. More importantly, the urchin-like CoP NCs present superior stability and keep their catalytic activity for at least 10 000 CV cycles for HER in 0.5 M H2SO4 and over 30 000 s for ORR in 0.1 M KOH, which is ascribed to their robust three-dimensional structure. This urchin-like CoP NCs might be a promising replacement to the Pt-based electrocatalysts in water splitting and fuel cells.
Electrochemical conversion of carbon dioxide (CO2) into high-value chemical products has become a dramatic research area because of the efficient exploitation of carbon resources and simultaneous ...reduction of atmospheric CO2 concentration. Herein, we report the bismuth-based catalyst in the efficient electroconversion of CO2 for the formation of formate with a maximum Faradaic efficiency of 91% and partial current density of ∼8 mA cm–2 at −0.9 V vs RHE. Experimental and theoretical results show that the bismuth–oxygen structure of bismuth oxides is beneficial for a higher adsorption of CO2 and the rate-determining route switching from the initial fast pre-equilibrium of electron transfer process to the subsequent hydrogenation step, accompanied by a lower free energy of intermediate. This work may offer valuable insights into crystal structure engineering to achieve efficient electrocatalysts for selective CO2 reduction toward generation of valuable products.
The aim of this study was to develop efficient anode materials for direct methanol fuel cell applications. The Ni foam was modified with Bi2O3 - acetylene black-rGO to increase catalytic activity ...toward methanol oxidation. The Bi2O3 was synthesized via a straightforward green technique. The characterization was achieved by using Fourier transform infrared spectroscopy and X-Ray diffraction analysis. The transmission electron microscope and field emission scanning electron microscope was utilized to evaluate the surface properties of catalysts, and energy-dispersive X-ray spectroscopy were employed to determine the chemical composition. Bi2O3 particles with diameters ranging from 15 to 75 nm were crystal structures in the (111), (220), (311), and (342) crystal planes. The performance of methanol electrooxidation in an alkaline medium was investigated using cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry techniques. The surface coverage of the redox species was 2.04 × 10−5 mol g−1, and the diffusion coefficient ranged between 8.02 × 10−12 and 1.25 × 10−13 cm2 s−1. According to the obtained results, the Bi2O3 - acetylene black-rGO modification enhanced the electrocatalytic activity of Ni foam against methanol oxidation in an alkaline medium.
•This research aimed to produce effective anode materials for methanol fuel cells.•Facile method was used to generate composite electrocatalyst.•Bi2O3- acetylene black-reduced graphene oxide supported Ni foam used.
PDF
