CeO2 for modulating the electronic structure of nickel-cobalt bimetallic phosphides to promote efficient overall water splitting

The discovery of earth-abundant electrocatalysts to replace platinum and iridium for overall water splitting is a crucial step in reducing the cost of green hydrogen production. Transition metal phosphides have drawn wide attention due to their non-toxicity, good chemical stability, low cost, and stable catalytic activity in alkaline electrolytes. We report a three-dimensional flower-like structure composed of core-shell nanoneedles as catalysts, in which CeO2 is introduced on the surface of nickel cobalt bimetallic phosphide through electrodeposition. And X-ray photoelectron spectroscopy testing and DFT calculations show electron coupling and transfer between CeO2 and CoP3, thereby modulating the electronic structure of the catalyst surface and reducing the adsorption energy of H atoms during the catalytic process, resulting in enhanced catalytic activity. In 1 M KOH, it exhibits a low overpotential of 109 and 296 mV to achieve the current density of 50 mA cm-2 for HER and OER, respectively. When used as both cathode and anode as a bifunctional catalyst, a voltage of only 1.77 V is required to achieve a current density of 50 mA cm-2, demonstrating great industrial potential.

Insights into the Distinct Behaviors between Bifunctional and Binary Organoborane Catalysts through Terpolymerization of Epoxide, CO2, and Anhydride

Alkyl borane compounds-mediated polymerizations have expanded to Lewis pair polymerization, free radical polymerization, ionic ring-opening polymerization, and polyhomologation. The bifunctional organoborane catalysts that contain the Lewis acid and ammonium or phosphonium salt in one molecule have demonstrated superior catalytic performance for ring-opening polymerization of epoxides and ring-opening copolymerization of epoxides and CO2 than their two-component analogues, i.e., the blend of organoborane and ammonium or phosphonium salt. To explore the origin of the differences of the one-component and two-component organoborane catalysts, here we conducted a systematic investigation on the catalytic performances of these two kinds of organoborane catalysts via terpolymerization of epoxide, carbon dioxide and anhydride. The resultant terpolymers produced independently by bifunctional and binary organoborane catalyst exhibited distinct microstructures, where a series of gradient polyester-polycarbonate terpolymers with varying polyester content were afforded using the bifunctional catalyst, while tapering diblock terpolymers were obtained using the binary system. The bifunctional catalyst enhances the competitiveness of CO2 insertion than anhydride, which leads to the premature incorporation of CO2 into the polymer chains and ultimately results in the formation of gradient terpolymers. DFT calculations revealed the role of electrostatic interaction and charge distribution caused by intramolecular synergistic effect for bifunctional organoborane catalyst.

MOF-derived Fe/Ni@C marigold-like nanosheets as heterogeneous electro-Fenton cathode for efficient antibiotic oxytetracycline degradation

The widespread occurrence of organic antibiotic pollution in the environment and the associated harmful effects necessitate effective treatment method. Heterogeneous electro-Fenton (hetero-EF) has been regarded as one of the most promising techniques towards organic pollutant removal. However, the preparation of efficient cathode still remains challenging. Herein, a novel metal-organic framework (MOF)-derived Fe/Ni@C marigold-like nanosheets were fabricated successfully for the degradation of oxytetracycline (OTC) by serving as the hetero-EF cathode. The FeNi3@C (Fe/Ni molar ratio of 1:3) based hetero-EF system exhibited 8.2 times faster OTC removal rate than that of anodic oxidation and possessed many advantages such as excellent OTC degradation efficiency (95.4% within 90 min), broad environmental adaptability (satisfactory treatment performance for multiple antibiotics under various actual water matrixes), good stability and reusability, and significant toxicity reduction. The superior hetero-EF catalytic performance was mainly attributed to: 1) porous carbon and Ni existence were both conducive to the in-situ generation of H2O2 from dissolved O2; 2) the synergistic effects of bimetals together with electron transfer from the cathode promoted the regeneration of ≡ FeII/NiII, thereby accelerating the production of reactive oxygen species; 3) the unique nanosheet structure derived from the precursor two-dimensional Fe-Ni MOFs enhanced the accessibility of active sites. This work presented a promising hetero-EF cathode for the electrocatalytic treatment of antibiotic-containing wastewaters.

Construction of Synergistic Co/CoO Interface to Enhance Hydrogenation Activity of Ethyl Lactate to 1,2-Propanediol

The development of effective and stable non-precious catalysts for hydrogenation of ester to diols remains a challenge. Herein, the catalytic hydrogenation of ethyl lactate (EL) to 1,2-propanediol (1,2-PDO) with supported Co catalysts derived from layered double hydroxides (LDHs) is investigated. Catalytic tests reveal that LDH-derived Co catalysts exhibit the best catalytic performance with 98 % of EL conversion and >99 % of 1,2-PDO selectivity at mild conditions, compared with other Co catalysts (supported on Al2 O3 , and TiO2 ) and LDH-derived Cu catalysts. Due to the strong interaction among Co and Al matrix, the main composition is metallic Co0 and CoO after reduction at 600 °C. Besides, the catalyst shows good recyclability in the liquid phase hydrogenation. The superior catalytic performance can be attributed to the synergistic effect between Co0 and CoO, in which H2 molecule is activated on Co0 and EL is strongly adsorbed on CoO via hydroxyl groups.

Curvature effects regulate the catalytic activity of Co@N4-doped carbon nanotubes as bifunctional ORR/OER catalysts

The advancement of metal-air batteries relies significantly on the development of highly efficient bifunctional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we investigate the potential application of Co@N4-doped carbon nanotubes (Co@N4CNTs) as bifunctional catalysts using density functional theory calculations. We explore the stability and electronic properties of Co@N4CNTs by analyzing energies, bond lengths, conducting ab initio molecular dynamics simulations, and examining the density of states. Notably, the diameter of the nanotubes has a notable impact on the catalytic performance of Co@N4CNTs. A remarkable 54% improvement in catalytic activity when transitioning from (4, 4) to (24, 4) Co@N4CNTs, with ηBi from changing from 1.40 to 0.64 V. We have several exceptional catalysts with low overpotentials, including (18, 4), (22, 4), and (24, 4) Co@N4CNTs, which exhibit ηBi values of 0.68, 0.67, and 0.64 V, respectively. Moreover, we link the increased activity of Co@N4CNTs to the change of Co atom's partial d orbital energy, facilitated by adjustments in the diameter of Co@N4CNTs. This revelation offers valuable insights into the underlying factors driving the enhancement of catalytic activity through alterations in orbital energy levels. Our research uncovers several excellent catalysts and provides valuable insights for the design and development of efficient catalysts for metal-air batteries.

Acid Etching Strategy: Optimizing Bifunctional Activities of Metal/Nitrogen-doped Carbon Catalysts for Efficient Rechargeable Zn-Air Batteries

Transition metal-embedded heteroatom carbon composites are regarded as an important branch of bifunctional catalysts for rechargeable Zn-air batteries. The inevitable transition metal particles on the carbon skeleton may affect the availability of the metal-heteroatom-carbon catalytic site. Herein, we propose an acid treatment strategy to remove the bare transition metal particles, thus regulating the electrochemical surface area. The OER activities are highly related to the electrochemical surface area for the catalysts with different acid treatment times. In addition, there exists an optimal acid treatment time to achieve the highest ORR and OER activities with the ΔE value of 0.75 V. Given the superior bifunctional activities after acid treatment, we further assemble the rechargeable Zn-air batteries with the optimal catalyst, which achieves a peak power density of 364 mW cm-2 and long cycling life of 500 h at 10 mA cm-2 . This work affords an efficient strategy to enhance the ORR/OER activities and may guide the design of transition metal/heteroatom carbon composites.

High entropy alloy nanoparticles as efficient catalysts for alkaline overall seawater splitting and Zn-air batteries

High entropy alloys (HEAs) are those metallic materials that consist of five or more elements. Compared with conventional alloys, they have much more catalytic active sites due to unique structural characteristics such as high entropy effect and lattice distortion, endowing them with promising applications in the region of hydrolysis catalysts. Herein, we successfully loaded high-entropy alloys onto carbon nanotubes (FeNiCoMnRu@CNT) by hydrothermal means. It exhibits excellent HER and OER properties in alkaline seawater. To accomplish two-electrode total water splitting when constructed into Zn air cells, it only needed 1.6 V, and the timing voltage curve showed a steady current density of 10 mA cm^-2 during constant electrolysis for more than 30 h in alkaline seawater. The remarkably high HER and OER activity of FeNiCoMnRu@CNT HEAs NPS indicates the potentially broad application prospect of HEAs for Zn air battery.

Metal-organic framework derived FeNi alloy nanoparticles embedded in N-doped porous carbon as high-performance bifunctional air-cathode catalysts for rechargeable zinc-air battery

Developing efficient and durable bifunctional air-cathode catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key efforts promoting the practical rechargeable zinc-air batteries (ZABs). In this paper, high-performance bifunctional air-cathode catalysts by a two-step strategy: atomically dispersed Ni on N-doped carbon is first derived from MOF to form uniformly dispersed NiNC, which are pyrolyzed together with Fe source at different high-temperatures to form FeNi@NC-T (T = 800, 900, and 1000 °C) catalysts. The as-synthesized non-noble metal FeNi@NC-900 catalyst exhibits a considerably small potential gap (ΔE) of 0.72 V between ORR and OER, which is as the same as commercial noble metal Pt/C + Ir black mixed catalyst. The performance of the ZABs using FeNi@NC-900 as the air-cathode catalyst displays a power density of 119 mW·cm^-2 and a specific capacity of 830.1 mAh·g^-1, which is superior to that of Pt/C + Ir black mixed catalyst. This work provides a guideline for designing alloy electrocatalysts with uniform size and nanoparticle distribution for metal-air batteries with bifunctional air-cathodes.

Pt modified NiMoO4-GO/NF nanorods withstrong metal-support interaction as efficient bifunctional catalysts for overall water splitting

Catalysts for the electrolysis of water are critical in the production of hydrogen for the energy industry. The use of strong metal-support interactions (SMSI) to modulate the dispersion, electron distribution, and geometry of active metals is an effective strategy for improving catalytic performance. However, in currently used catalysts, the supporting effect does not significantly contribute directly to catalytic activity. Consequently, the continued investigation of SMSI, using active metals to stimulate the supporting effect for catalytic activity, remains very challenging. Herein, the atomic layer deposition technique was employed to prepare an efficient catalyst composed of platinum nanoparticles (Pt NPs) deposited on nickel-molybdate (NiMoO₄) nanorods. Nickel-molybdate's oxygen vacancies (V_o) not only help anchor highly-dispersed Pt NPs with low loading but also strengthen the SMSI. The valuable electronic structure modulation between Pt NPs and V_o resulted in a low overpotential of the hydrogen and oxygen evolution reactions, returning results of 190 mV and 296 mV, respectively, at a current density of 100 mA cm^-2 in 1 M KOH. Ultimately, an ultralow potential (1.515 V) for the overall decomposition of water was achieved at 10 mA cm^-2, outperforming state-of-art catalysts based on the Pt/C || IrO₂ couple (1.668 V). This work aims to provide reference and a concept for the design of bifunctional catalysts that apply the SMSI effect to achieve a simultaneous catalytic effect from the metal and its support.

MOF-Derived Co and Fe Species Loaded on N-Doped Carbon Networks as Efficient Oxygen Electrocatalysts for Zn-Air Batteries

HIGHLIGHTS

A novel method is developed to prepare bifunctional oxygen electrocatalysts composed of Co nanoparticles and highly dispersed Fe loaded on N-doped carbon substrates by virtues of metal-organic frameworks and two different doping processes. The designed catalysts show comparable performance with commercial catalysts. Meanwhile, rechargeable Zn-air batteries with prepared catalysts demonstrate high peak power density and good cycling stability. The performance promotion originates from the synergy between Co nanoparticles and highly dispersed Fe, porous structures, large specific areas, and distinct three-dimensional carbon networks.  .

ABSTRACT

Searching for cheap, efficient, and stable oxygen electrocatalysts is vital to promote the practical performance of Zn-air batteries with high theoretic energy density. Herein, a series of Co nanoparticles and highly dispersed Fe loaded on N-doped porous carbon substrates are prepared through a “double-solvent” method with in situ doped metal-organic frameworks as precursors. The optimized catalysts exhibit excellent performance for oxygen reduction and evolution reaction. Furthermore, rechargeable Zn-air batteries with designed catalysts demonstrate higher peak power density and better cycling stability than those with commercial Pt/C+RuO₂. According to structure characterizations and electrochemical tests, the interaction of Co nanoparticles and highly dispersed Fe contributes to the superior performance for oxygen electrocatalysis. In addition, large specific surface areas, porous structures and interconnected three-dimensional carbon networks also play important roles in improving oxygen electrocatalysis. This work provides inspiration for rational design of advanced oxygen electrocatalysts and paves a way for the practical application of rechargeable Zn-air batteries. [Image: see text]

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40820-022-00890-w.

Metal-organic frameworks/ hydrotalcite/graphene oxide sandwich composites derived Fe-Ce@GSL hierarchical materials as highly efficient catalysts for rechargeable Zn-air batteries

The fabrication of efficient bi-functional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) applied in energy storage and conversion devices like Zn-air batteries to solve the growing energy and environmental crises has attracted great attentions. In this work, the Fe-Ce@GSL catalysts have developed by first constructing the MOF/LDH/GO templates with multi-stage mixed growth method followed by calcining the template at high temperature. Fe-Ni-LDH (hydrotalcite) plays the role of linking the metal organic frameworks (Fe-Ce-MOF) and graphene oxides (GO), avoiding the separation of MOFs derivatives and GO sheets during pyrolysis process. Rare-earth metal oxide (CeO₂) featuring with abundant oxygen vacancies dispersed on the surface of transition-metal oxide can efficiently improve the stability of catalysts. The optimal Fe₇-Ce₁@GSL-800 catalysts exhibit excellent ORR/OER performances with the potential gap between ORR (E_1/2 = 0.87 V) and OER (E_J=10 = 1.59 V) of 0.720 V. The aqueous Zn-air battery assembled with Fe₇-Ce₁@GSL-800 catalysts exhibits outstanding performances with high open circuit voltage (1.56 V), large specific capacity (801.1 mAh/g@10 mA.cm^-2), and good charge-discharge cycle performances (>500 h). The Fe₇-Ce₁@GSL-800 based solid-state Zn-air battery also delivers an excellent performance with high specific capacity (791.7 mAh/g@5 mA.cm^-2) and long cycle stability (>230 h).

Single Ir atom anchored in pyrrolic-N4 doped graphene as a promising bifunctional electrocatalyst for the ORR/OER: a computational study

The development of highly-efficient electrocatalysts with bifunctional catalytic activity for oxygen reduction reaction (ORR) and oxygen evolution reaction. (OER) still remains a great challenge for the large-scale application of renewable energy conversion and storage technologies. Herein, by means of comprehensive density functional theory (DFT) computations, we systematically explored the potential of pyrrolic-N doped graphene (pyrrolic-N₄-G) supported various transition metal atoms (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Pd, W, Os, Ir, and Pt) as electrocatalysts for the ORR and OER. Our results revealed that these TM/pyrrolic-N₄-G candidates exhibit high electrochemical stability due to their positive dissolution potentials. Especially, the Ir/pyrrolic-N₄-G can perform as a promising bifunctional electrocatalyst for both ORR and OER with the low overpotentials (η^ORR = 0.34 V and η^OER = 0.32 V). Interestingly, multiple-level descriptors, including energy descriptor (ΔG_OH* - ΔG_O*), (ΔG_OH*), structure descriptor (φ), and d-band center (ε) can well rationalize the origin of the high catalytic activity of Ir/pyrrolic-N₄-G for the ORR/OER. Our findings not only further enrich the SACs, but also open a new avenue to develop novel 2D materials-based SACs for highly efficient oxygen electrocatalysts.

Carbon-based 0D/1D/2D assembly with desired structures and defect states as non-metal bifunctional electrocatalyst for zinc-air battery

For the design of electrocatalysts, the combination between components and the regulation of material structures tend to be neglected, giving rise to the constraint of catalytic performance and durability. Herein, we developed a graphene oxide quantum dots (GOQDs) with enhanced oxygen content by a one-step cutting method. Then, one-dimensional (1D) carbon nanotubes and two-dimensional (2D) reduced graphene oxide are crosslinked and self-assembled, thus attracting unsaturated-bond-riches GOODs (0D) to uniformly attach to the skeleton, simultaneously achieving nitrogen and sulfur co-doping. To the best of our knowledge, there is no report to prepare bifunctional electrocatalyst with GOQDs. Electrochemical tests show that even without metal-doping, the novel non-metal bifunctional electrocatalyst (N,S-GOQD-RGO/CNT) exhibits a higher half-wave potential (0.84 V) and enhanced limiting current density (5.88 mA cm^-2) than commercial Pt/C catalyst. The density functional theory is implemented to reveal the coordination of nitrogen and sulfur co-doping on GOQDs, which results in the improvement of overall catalytic active sites. Furthermore, the rechargeable zinc-air battery based on N,S-GOQD-RGO/CNT exhibits a maximum power density of 134.3 mW cm^-2, open circuit potential of 1.414 V, which is better than Pt/C+Ru/C mixed material. The obtained N,S-GOQD-RGO/CNT will provide a perspective application in fuel cells.

Highly ordered micro-meso-macroporous Co-N-doped carbon polyhedrons from bimetal-organic frameworks for rechargeable Zn-air batteries

Rational design of non-precious metal catalysts for efficient oxygen reduction and oxygen evolution reactions (ORR/OER) is important for rechargeable metal-air batteries. Building highly ordered porous structures while maintaining their overall crystalline orderliness is highly desirable, but remains an arduous challenge. Here, we have synthesized bimetallic metal-organic frameworks (MOFs) on highly ordered three-dimensional (3D) polystyrene templates by controlling the nucleation process. The ordered macropores with 190 nm diameters were uniformly distributed on the as-prepared ZnCo zeolitic imidazolate framework (ZnCo-ZIF). Afterwards, 3D ordered micro-meso-macroporous Co-N-doped carbon polyhedrons (3DOM Co-NCPs) was developed by calcination. With the synergy of the highly dispersed CoNC catalytic sites and the distinct porous structure, the synthesized 3DOM Co-NCPs exhibit impressive bifunctional activity. Additionally, the 3DOM Co-NCPs-900 for Zn-air battery exhibits extraordinary power density, high energy density, and acceptable stability. This approach offers a useful strategy for the fabrication of highly efficient electrocatalysts with 3D ordered porous.

Bifunctional Catalysts Containing Zn(II) and Imidazolium Salt Ionic Liquids for Chemical Fixation of Carbon Dioxide

Zn(II) can efficiently promote the catalytic performance of imidazolium salt ionic liquids (imi-ILs) for the chemical fixation of CO₂ into epoxides. To obtain sustainability, immobilized bifunctional catalysts containing both imi-ILs and Zn(II) were prepared using bimodal mesoporous silica (BMMs) as carrier, through grafting of Zn(OAc)₂ and 1-(trimethoxysilyl)propyl-3-methylimidazolium chloride (Si-imi) separately in the nanopores. The catalysts, named as BMMs-Zn&ILs, were identified as efficient catalysts for cycloaddition reaction of CO₂ into epoxides under solvent-free conditions. BMMs-Zn&ILs showed good catalytic activity, which increased with the increase of the molar ratio of Zn(II) to Si-imi. As a comparison, different catalytic systems including homogeneous imi-IL, BMMs-ILs and BMMs-Zn were studied to demonstrate different cooperation behaviors. Furthermore, the kinetics studies of homogeneous and heterogeneous bifunctional catalysts were employed to confirm the differences, as well as to support the proposed cooperative catalysis mechanism in the nanopores.

Montmorillonite-catalyzed conversions of carbon dioxide to formic acid: Active site, competitive mechanisms, influence factors and origin of high catalytic efficiency

Design of heterogeneous catalysts for CO₂ conversions to value-added chemicals is highly desirable. Montmorillonite and other clay minerals have been used widely in catalytic reactions including CO₂ hydrogenation, while a molecular-level understanding remains lacking. In this study, periodic density functional theory calculations are employed and a comprehensive understanding about montmorillonite-catalyzed CO₂ hydrogenation to formic acid is given, including active site, mechanism, influence factors, competitive reaction paths, and origin of superior catalysis. Catechol that is readily available and can also be considered as a fragment of abundantly distributed humic substances is an effective hydrogen source. The penta-coordinated M³⁺ (M²⁺) sites of edge surfaces are active sites, and reactions occur preferentially at M²⁺ rather than M³⁺ sites. The catalytic activities depend strongly on the identity of M²⁺ (M³⁺) cations, and all reaction paths follow the concerted mechanisms transferring two hydrogen atoms in one step, with those producing formate being highly preferred. M²⁺/Al³⁺ substitutions and substituent effects are two critical factors to affect catalytic activities, and with synergy of Mg²⁺/Al³⁺ substitutions and -NMe₂ substituent, reactions are exergonic (-0.09 eV) and activation barriers are so low (0.48 eV) that formate can be facilely produced at ambient conditions. Edge surfaces of clay minerals are bifunctional catalysts, with M²⁺ cations showing Lewis acids and MOH groups playing similar effects as basic additives. Results provide new insights about heterogeneous catalysis of CO₂ hydrogenation and other reactions.

Assessment of the Location of Pt Nanoparticles in Pt/zeolite Y/γ-Al2O3 Composite Catalysts

The location of Pt nanoparticles was studied in Pt/zeolite Y/γ-Al2O3 composite catalysts prepared by H2PtCl6 ⋅ 6H2O (CPA) or Pt(NH3)4(NO3)2 (PTA) as Pt precursors. The aim of this study is to validate findings from Transmission Electron Microscopy (TEM) by using characterization techniques that sample larger amounts of catalyst per measurement. Quantitative X-ray Photoelectron Spectroscopy (XPS) showed that the catalyst prepared with CPA led to a significantly higher Pt/Al atomic ratio than the catalyst prepared with PTA confirming that the 1-2 nm sized Pt nanoparticles in the former catalyst were located on the open and mesoporous γ-Al2O3 component, whereas they were located in the micropores of zeolite Y in the latter. By using infrared spectroscopy, a shift in the absorption band maximum of CO chemisorbed on Pt nanoparticles was observed, which can be attributed to a difference in electronic properties depending on the support of the Pt nanoparticles. Finally, model hydrogenation experiments were performed using β-phenylcinnamaldehyde, a reactant molecule with low diffusivity in zeolite Y micropores, resulting in a 5 times higher activity for the catalyst prepared by CPA compared to PTA. The combined use of these characterization techniques allow us to draw more robust conclusions on the ability to control the location of Pt nanoparticles by using either CPA or PTA as precursors in zeolite/γ-Al2O3 composite catalyst materials.

Selective electrochemical H2O2 generation and activation on a bifunctional catalyst for heterogeneous electro-Fenton catalysis

Heterogeneous electro-Fenton is attractive for pollutants removal, where H₂O₂ is in-situ generated and simultaneously activated to ·OH at the cathodic catalyst. However, the heterogeneous electro-Fenton efficiency is limited by low H₂O₂ production and slow Fe(II) regeneration, which can be improved by tuning oxygen reduction selectivity and facilitating electron transfer to Fe(III) centers. Herein, we designed a bifunctional catalyst with FeOx nanoparticles embedded into N-doped hierarchically porous carbon (FeOx/NHPC). The activity and selectivity for H₂O₂ production were improved by regulating N doping configurations and contents. The obtained FeOx/NHPC750 presented high catalytic activity for H₂O₂ production with a low overpotential of 190 mV and high H₂O₂ selectivity of 95%˜98% at -0.3 V to -0.8 V. The Fe(II) regeneration was enhanced by the strong interfacial interaction between FeOx and N-doped porous carbon support, which leaded to a rapid decomposition of H₂O₂ into ·OH. FeOx/NHPC750 exhibited excellent electro-Fenton performance for the degradation and mineralization of phenol, sulfamethoxazole, atrazine, rhodamine B and 2,4-dichlorophenol in neutral reaction solution. This study offered a new strategy to construct an efficient and durable bifunctional catalyst for heterogeneous electro-Fenton system for advanced treatment of refractory wastewater.

Prompt Electrodeposition of Ni Nanodots on Ni Foam to Construct a High-Performance Water-Splitting Electrode: Efficient, Scalable, and Recyclable

In past decades, Ni-based catalytic materials and electrodes have been intensively explored as low-cost hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts for water splitting. With increasing demands for Ni worldwide, simplifying the fabrication process, increasing Ni recycling, and reducing waste are tangible sustainability goals. Here, binder-free, heteroatom-free, and recyclable Ni-based bifunctional catalytic electrodes were fabricated via a one-step quick electrodeposition method. Typically, active Ni nanodot (NiND) clusters are electrodeposited on Ni foam (NF) in Ni(NO3)2 acetonitrile solution. After drying in air, NiO/NiND composites are obtained, leading to a binder-free and heteroatom-free NiO/NiNDs@NF catalytic electrode. The electrode shows high efficiency and long-term stability for catalyzing hydrogen and oxygen evolution reactions at low overpotentials (10ηHER = 119 mV and 50ηOER = 360 mV) and can promote water catalysis at 1.70 V@10 mA cm-2. More importantly, the recovery of raw materials (NF and Ni(NO3)2) is quite easy because of the solubility of NiO/NiNDs composites in acid solution for recycling the electrodes. Additionally, a large-sized (S ~ 70 cm2) NiO/NiNDs@NF catalytic electrode with high durability has also been constructed. This method provides a simple and fast technology to construct high-performance, low-cost, and environmentally friendly Ni-based bifunctional electrocatalytic electrodes for water splitting.