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The replacement of noble-metal-based electrocatalysts with earth-abundant, low-cost bifunctional electrocatalysts for efficient hydrogen generation is required. Herein, an amorphous and porous 2D N...

A copper phosphide (Cu3P) thin film is synthesized on a Ni foam using a one-step electrodeposition method at room temperature and annealed at 300 °C in Ar atmosphere. The Cu3P film is amorphous and has a flat morphology with surface voids. It works as an electrocatalyst for water oxidation in an alkaline 1 M KOH electrolyte. It exhibits excellent catalytic oxygen evolution reaction with an overpotential of 310 mV, Tafel slope of 88 mV/dec, and good stability over 20 h of operation at 10 mA/cm2. The excellent OER performance is due to its large electrochemically active surface area and low charge transfer resistance at the catalyst-electrolyte interface after the annealing.

Porous iron–nickel hydroxyphosphate and iron–cobalt hydroxyphosphate electrodes are prepared by one-step electrodeposition method. The as-prepared iron–nickel hydroxyphosphate and iron–cobalt hydroxyphosphate electrodes show excellent performance for water splitting with high catalytic activity towards the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), with a lower overpotential of 220 and 235 mV for the OER and 145 and 160 mV for the HER, respectively. Moreover, two-electrode electrolyzer using iron-nickel hydroxyphosphate as both the anode and cathode requires a cell voltage of 1.65 V while iron–cobalt hydroxyphosphate requires cell voltage of 1.67 V to gain current density of 10 mA cm−2.

High-density CuCo2O4 nanosheets are grown on Ni foam using electrodeposition followed by air annealing for a Li-ion battery anode. The anode exhibits a high discharge capacity of 1244 mAh/g at 0.1 A/g (82% coulombic efficiency) and excellent high-rate performance with 95% capacity retention (1100 mAh/g after 200 cycles at 1 A/g). The outstanding battery performance of the CuCo2O4 anode is attributed to its binder-free direct contact to the current collector and high-density nanosheet morphology. The present experimental findings demonstrate that the electrodeposited binder-free CuCo2O4 material may serve as a safe, low-cost, long-cycle life anode for Li-ion batteries.

Low-cost and competent electrocatalysts play a key role in an electrocatalytic water oxidation reaction. Herein, we report that readily available bare nickel foam (NF) can be used as conductive substrate and precursor to grow a porous nickel oxide (NiO) using a simple and scalable thermal oxidation method. The obtained NiO supported on NF is used as binder-free electrocatalyst for the oxygen evolution reaction (OER) and its electrochemical properties are evaluated by linear sweep voltammetry (LSV) in 1 M KOH. The porous NiO thin film acts as an efficient electrocatalyst for the OER and achieves a catalytic current density of 10 mA cm−2 at an overpotential of 310 mV with a smaller Tafel slope of 54 mV dec−1. The electrode also shows good durability over 24 h with negligible degradation. This durable and high-performance electrocatalyst can be a competitor to electrocatalysts that consist of costly elements and, require advanced synthesis; the NiO electrocatalyst shows progress towards the replacement of noble metal-based electrocatalysts for the OER.

The development of an inexpensive, stable, and highly active electrocatalyst for oxygen evolution reaction (OER) is essential for the practical application of water splitting. Herein, we have synthesized an electrodeposited cobalt hydroxide on nickel foam and subsequently annealed in an air atmosphere at 400 °C for 2 h. In-depth characterization of all the films using X-ray diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) techniques, which reveals major changes for their structural, morphological, compositional and electrochemical properties, respectively. The cobalt hydroxide nanosheet film shows high catalytic activity with 290 mV overpotential at 10 mA cm −2 and 91 mV dec −1 Tafel slope and robust stability (24 h) for OER in 1 M KOH electrolyte compared to cobalt oxide (340 mV). The better OER activity of cobalt hydroxide in comparison to cobalt oxide originated from high active sites, enhanced surface, and charge transport capability.

Nanostructured iron oxyhydroxide (FeOOH) thin films have been synthesized using an electrodeposition method on a nickel foam (NF) substrate and effect of air annealing temperature on the catalytic performance is studied. The as-deposited and annealed thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and linear sweep voltammetry (LSV) to determine their structural, morphological, compositional and electrochemical properties, respectively. The as-deposited nanostructured amorphous FeOOH thin film is converted into a polycrystalline Fe2O3 with hematite crystal structure at a high temperature. The FeOOH thin film acts as an efficient electrocatalyst for the oxygen evolution reaction (OER) in an alkaline 1 M KOH electrolyte. The film annealed at 200 °C shows high catalytic activity with an onset overpotential of 240 mV with a smaller Tafel slope of 48 mV/dec. Additionally, it needs an overpotential of 290 mV to the drive the current density of 10 mA/cm2 and shows good stability in the 1 M KOH electrolyte solution.

Cu(OH) 2 and CuO nanowires (NWs) are synthesized using a chemical-oxidation technique followed by thermal annealing. These NWs electrodes show excellent electrocatalytic performances with a maximum current density above 50 A g −1 at 0.6 V and good long-term electrochemical stabilities towards methanol electro-oxidation, compared with other copper based transition-metal oxide electrocatalysts. The excellent electrocatalytic properties of the materials are due to the direct in-situ growth of an electroactive nanostructure that enhances mechanical adhesion and facilitates a fast electron transfer between the current collector and the NWs electrocatalyst.

A high activity of a two-dimensional (2D) copper oxide (CuO) electrocatalyst for the oxygen evolution reaction (OER) is presented. The CuO electrode self-assembles on a stainless steel substrate via chemical bath deposition at 80 °C in a mixed solution of CuSO4 and NH4OH, followed by air annealing treatment, and shows a 2D nanosheet bundle-type morphology. The OER performance is studied in a 1 M KOH solution. The OER starts to occur at about 1.48 V versus the RHE (η = 250 mV) with a Tafel slope of 59 mV dec−1 in a 1 M KOH solution. The overpotential (η) of 350 mV at 10 mA cm−2 is among the lowest compared with other copper-based materials. The catalyst can deliver a stable current density of >10 mA cm−2 for more than 10 hours. This superior OER activity is due to its adequately exposed OER-favorable 2D morphology and the optimized electronic properties resulting from the thermal treatment.

Efficient and low‐cost multifunctional electrodes play a key role in improving the performance of energy conversion and storage devices. In this study, ultrathin nanoporous CuCo2O4 nanosheets are synthesized on a nickel foam substrate using electrodeposition followed by air annealing. The CuCo2O4 nanosheet electrode exhibits a high specific capacitance of 1473 F g─1 at 1 A g─1 with a capacity retention of ∼93% after 5000 cycles in 3 M KOH solution. It also works well as an efficient oxygen evolution reaction electrocatalyst, demonstrating an overpotential of 260 mV at 20 mA cm─2 with a Tafel slope of ∼64 mV dec─1. in 1 M KOH solution, which is the lowest reported among other copper-cobalt based transition metal oxide catalysts. The catalyst is very stable at >20 mA cm─2 for more than 25 h. The superior electrochemical performance of the CuCo2O4 nanosheet electrode is due to the synergetic effect of the direct growth of 2D nanosheet structure and a large electrochemically active surface area associated with nanopores on the CuCo2O4 nanosheet surface.

Currently, electronic waste (e-waste) is the world’s most challenging and rapidly growing problem in the waste stream. To develop an alternative way to use e-waste (waste copper (Cu) wires) to accelerate the oxygen evolution reaction (OER) of water electrolysis, the waste Cu wires are used as a low-cost current collector. We demonstrate a simple electrodeposition process to deposit nickel-iron hydroxide (NiFe LDH) nanosheets on self-supported copper hydroxide (Cu(OH)2/Cu) nanowires grown via chemical-oxidation on waste Cu wire. Benefiting from the efficient electron transport, high mass activity, and surface area this electrocatalyst exhibits an efficient OER performance with a low overpotential of 275 mV and 390 mV at 20 and 100 mA cm−2 respectively, with excellent stability. This work provides a promising pathway to recycle e-waste into value-added resources in various energy conversion applications.

The development of efficient and earth-abundant electrocatalysts for overall water splitting is important but still challenging. Herein, iron phosphate (FePi) electrode is synthesized using a successive ionic layer deposition and reaction (SILAR) method on a nickel foam substrate at room temperature and is used as a bifunctional electrocatalyst for water splitting. The prepared FePi electrodes show excellent electrocatalytic activity and stability for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The FePi electrode exhibits low overpotential of 230 mV and 157 mV towards the OER and HER, respectively, with superior long-term stability. As a result, an electrolyzer that exploits FePi as both the anode and the cathode is constructed, which requires a cell potential of 1.67 V to deliver a 10 mA cm−2 current density in 1 M KOH solution. The exceptional features of the catalyst lie in its structure and active metal sites, increasing surface area, accelerated electron transport and promoted reaction kinetics. This study may provide a facile and scalable approach to design a high-efficiency, earth-abundant electrocatalyst for water splitting.

Cu2ZnSnS4 (CZTS) absorbers have been grown on Mo-coated glass substrates by the rapid thermal processing (RTP) sulfurization of stacked metallic precursor (CZT) films at different annealing temperatures ranging from 500 to 580 °C for 5 min in sulfur atmosphere. The effects of sulfurization temperature on the structural, morphological, chemical, and optical properties of the CZTS absorbers have been investigated. XRD and Raman studies reveal that the as-deposited stacked metallic precursor films consist of metal elements such as Zn, Sn and binary alloys such as Cu6Sn5, Cu3Sn and CuZn. The sulfurized CZTS absorber films have single phase polycrystalline kesterite crystal structure with dense morphology. At 580 °C, the CZT metallic precursor film is fully sulfurized with Zn-rich and Sn-poor composition, and its bandgap energy is found to be 1.50 eV. The solar cell fabricated with the CZTS absorber grown at an optimized sulfurization temperature of 580 °C shows a conversion efficiency of ~5% for a 0.44 cm2 area with Voc=561 mV, Jsc=18.4 mA/cm2, and FF=48.2.

The Cu2ZnSnS4 (CZTS) thin films have been electrochemically deposited from a weak acidic medium (pH 4.50~5.00) onto Mo- coated and ITO-coated glass substrate by using single-step electrodeposition method. Trisodium citrate was used as a complexing agent. The effect of annealing atmospheres such as Ar, N2, N2+H2S on the structural, morphological, compositional, and optical properties of CZTS thin films has been investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and optical absorption techniques, respectively. XRD studies reveal that the as-deposited CZTS film is amorphous in nature. Upon annealing in different atmospheres, a relatively more intense and sharper diffraction peaks (112), (200), (220), and (312) of kesterite crystal structure with uniform and densely packed surface morphology are observed in N2+H2S atmosphere. Absorption study shows that the band gap energy of as-deposited CZTS thin film is 2.8 eV whereas after annealing, it is found to be 1.48, 1.76, and 1.53 eV for Ar, N2, N2+H2S atmospheres.

Nanostructured nickel zinc ferrite (NZF) thin films were synthesized via chemical deposition method (CDM). This deposition process was based on the thermal decomposition of ammonia complex ions at 328 K. The pH of the bath solution was varied from 9.8, 9.9 and 10.0 to study its effect on the structural, morphological and electrochemical properties. The structural studies of oxide films were carried out using X-ray diffraction and FT-IR technique. All studies indicate nickel zinc ferrite phase formation with spinel crystal structure having improved intensity at increasing pH. Scanning electron microscopy reveals that morphology gets changed from grain like to hexagonal flakes which also increased the surface-to-volume ratio. The contact angle was improved from hydrophilic to super hydrophilic due to porous nature. Along with this, to propose NZF thin films for possible application in energy storage devices, its electrochemical supercapacitor properties have been studied in aqueous KOH electrolyte. The NZF thin film synthesized at pH 9.9 have shown high specific capacitance of 67 Fg−1.

The Cu2ZnSnS4 (CZTS) thin films have been electrochemically deposited on Mo-coated glass substrate from weak acidic medium (pH 4.5–5) at room temperature. The effect of complexing agent (tri-sodium citrate) on the structural, morphological and compositional properties of CZTS thin films has been investigated. The as-deposited and annealed thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM),EDAX and X-ray photoelectron spectroscopy (XPS) techniques for their structural, morphological, compositional and chemical properties, respectively. XRD studies reveal that the amorphous nature of as-deposited thin film changes into polycrystalline with kesterite crystal structure after annealing in Ar atmosphere. The film prepared without complexing agent showed well-covered surface morphology on the substrate with some cracks on the surface of the film whereas those prepared using complexing agent, exhibited uneven and slightly porous and some overgrown particles on the surface of the films. After annealing, morphology changes into the flat grains, uniformly distributed over the entire surface of the substrate. The EDAX and XPS study reveals that the films deposited using 0.2 M tri-sodium citrate are nearly stoichiometric.

The Cu 2 ZnSnS 4 (CZTS) thin films have been electrodeposited onto the Mo coated and ITO glass substrates, in potentiostatic mode at room temperature. The deposition mechanism of the CZTS thin film has been studied using electrochemical techniques like cyclic voltammetery. For the synthesis of these CZTS films, tri-sodium citrate and tartaric acid were used as complexing agents in precursor solution. The structural, morphological, compositional, and optical properties of the CZTS thin films have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), EDAX and optical absorption techniques respectively. These properties are found to be strongly dependent on the post-annealing treatment. The polycrystalline CZTS thin films with kieserite crystal structure have been obtained after annealing as-deposited thin films at 550 in Ar atmosphere for 1 h. The electrosynthesized CZTS film exhibits a quite smooth, uniform and dense topography. EDAX study reveals that the deposited thin films are nearly stoichiometric. The direct band gap energy for the CZTS thin films is found to be about 1.50 eV. The photoelectrochemical (PEC) characterization showed that the annealed CZTS thin films are photoactive.

The effect of [Ga]/[Cd] ratio on the structural, morphological, optical and electrical properties of chemically sprayed Ga-doped CdO thin films is investigated. XRD studies reveal that the films are polycrystalline with cubic structure and exhibit (2 0 0) preferential orientation. It is inferred that the Ga 3+ ions replace the lattice sites at lower concentrations and interstitial sites at high concentrations. There is considerable broadening of (2 0 0) peak and shift of Bragg's angle with respect to [Ga]/[Cd] ratio. The electrical studies confirm degenerate, n-type semiconductor nature of Ga-doped CdO thin films with minimum resistivity of 3.7 × 10 −4 Ω cm. The optical gap varies from 2.27 to 2.44 eV due to Moss–Burstein effect. The highest figure of merit observed in the present study is 1.69 × 10 −4 Ω −1 . PL intensity of green emission around 470 nm has found to be increased with increase in [Ga]/[Cd] ratio.

Highly efficient and stable electrocatalysts from inexpensive and earth-abundant elements are emerging materials in the overall water splitting process. Herein, cobalt iron hydroxide nanosheets are directly deposited on nickel foam by a simple and rapid electrodeposition method. The cobalt iron hydroxide (CoFe/NF) nanosheets not only allow good exposure of the highly active surface area but also facilitate the mass and charge transport capability. As an anode, the CoFe/NF electrocatalyst displays excellent oxygen evolution reaction catalytic activity with an overpotential of 220 mV at a current density of 10 mA cm-2 . As a cathode, it exhibits good performance in the hydrogen evolution reaction with an overpotential of 110 mV, reaching a current density of 10 mA cm-2 . When CoFe/NF electrodes are used as the anode and the cathode for water splitting, a low cell voltage of 1.64 V at 10 mA cm-2 and excellent stability for 50 h are observed. The present work demonstrates a possible pathway to develop a highly active and durable substitute for noble metal electrocatalysts for overall water splitting.

Cu2ZnSnS4 (CZTS) thin films were deposited onto Mo-coated and tin-doped indium oxide (ITO) coated glass substrates by using single step electrodeposition technique followed by annealing in N2 + H2S atmosphere. Subsequently, they were applied to the fabrication of thin film solar cells. Upon annealing, the amorphous nature of as-deposited precursor film changes into polycrystalline kesterite crystal structure with uniform and densely packed surface morphology. Energy dispersive X-ray spectroscopy (EDS) study reveals that the deposited thin films are nearly stoichiometric. Optical absorption study shows the band gap energy of as-deposited CZTS thin films is 2.7 eV whereas, after annealing, it is found to be 1.53 eV. The solar cell fabricated with CZTS absorber layer, showed the best conversion efficiency (η) 1.21% for 0.44 cm2 with open-circuit voltage (V oc) = 315 mV, short-circuit current density (J sc) = 12.27 mA/cm2 and fill factor (FF) = 0.31.