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The catalytic performance and the stability of the water electrolysis system have perplexed the practical splitting water. Herein, 3D‐printed metallic electrodes with Janus porosity are reported, which can achieve the efficient bubble emission and provide high surface area. After a further one‐step treatment, the catalysts of Ru–Ni(OH)2 and Fe–Ni(OH)2 nanoarrays are in situ grown on the electrodes. Theoretical calculations and systematical experiments confirm the synergistic effect of the gradient morphology and the in situ grown catalysts. The electrolyzer shows unprecedented activity with an overpotential of 98 mV for hydrogen evolution reaction and 343 mV for oxygen evolution reaction at the current density of 500 mA cm−2 and outperformed stability, which can deliver 500 mA cm−2 at the voltage of 1.638 V for 2100 h with no significant decay, far exceedingly most state‐of‐the‐art electrolyzers. This 3D electrode with controllable bubble motions offers a viable solution for future industrial sustainable hydrogen production technology. [ABSTRACT FROM AUTHOR]

The lattice‐oxygen‐mediated mechanism is considered as a reasonable mechanism for the electrochemical catalytic oxygen evolution reaction (OER) of NiFe layered double hydroxides (LDHs). A NiFe LDH with distinct lattice contraction and microcrystallization was synthesized via a simple one‐step method using sodium gluconate. The lattice contraction is attributed to the interaction of carbon in sodium gluconate and iron in NiFe LDH. The NiFe LDH with optimized microcrystallization and lattice contraction shows a low overpotential of 217 mV at a current density of 10 mA cm−2 and excellent durability of 20 h at a high current density of 100 mA cm−2. The results revealed that a contractive metal–oxygen bond could boost the intrinsic activity of active sites and the microcrystallization promotes an increase in the number of active sites in terms of unit area. The chemical environment of oxygen elemental characterization and resistance at different chronopotentiometry times confirm that the lattice oxygen element is indeed involved in the process of OER, supporting the lattice‐oxygen‐mediated mechanism of NiFe LDH. Density functional theory calculations reveal that contractive metal–oxygen bonds induced a reduction of the adsorption energy barrier of intermediate products, thus improving the intrinsic catalytic activity. The special characteristics of microcrystallization and lattice contraction of NiFe LDH provide a strategy to improve both the number and the intrinsic activity of active sites in a versatile manner. [ABSTRACT FROM AUTHOR]

Electrocatalytic overall water splitting is a sustainable approach to realizing the clean production of hydrogen energy; however, it is mainly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). For large-scale hydrogen production, it is great urgent to develop efficient and low-cost OER electrocatalyst candidates from commercial noble metal-based materials. Herein, a facile template method was proposed for the preparation of a series of hierarchical NiFeV hydroxide nanotubes. With the combined advantages of a hierarchical nanostructure and the synergistic effect among multi-metal elements, the ternary hydroxides delivered outstanding OER performance. In particular, a low overpotential of 256.5 mV delivering a current density of 10 mA cm−2 with a Tafel slope of 52.4 mV dec−1 was achieved by hierarchical NiFeV hydroxide nanotubes with an initial Ni/Fe/V feed ratio of 8 : 1 : 1. After a subsequent topotactic transformation, ternary phosphide (denoted as NiFeVP) was obtained with the hierarchical nanostructure well maintained, and it achieved further performance enhancement where an overpotential of only 209.5 mV was required to deliver 10 mA cm−2 with a lower Tafel slope of 30.3 mV dec−1 and excellent durability for 50 h for chronopotentiometry even at 50 mA cm−2, demonstrating an admirable OER electrocatalyst. [ABSTRACT FROM AUTHOR]

Strategy of anchoring alloy nanoparticles made up of the efficient catalytic element (e.g., Ni, Fe) on dodecyl sulfate (DS‐)‐intercalated NiFe layered double hydroxides (DS‐‐NiFe LDH) obtained by a convenient one‐step hydrothermal coprecipitation method for essentially enhancing oxygen evolution reaction (OER) performance was proposed. The results of structural characterization indicate Pt2FeNi alloy nanoparticles evenly distribute on the surface of DS‐‐NiFe LDH. The sizes of the Pt2FeNi nanoparticles, closely related to their OER performance, could be well‐controlled by adjusting the amount of H2PtCl6 addition. The composite structure of as‐prepared product was stable during processes of synthesis, exfoliation, self‐assembly, and subsequent electrocatalytic OER. Rigorous electrochemical test proving the contributing catalytic active sites was located at the interface between Pt2FeNi and DS‐‐NiFe LDH, and the Ni and Fe were the major active elements while O atoms are adsorption sites. The formation of Pt2FeNi nanoparticles could greatly prompt the reduction of Tafel slope. The best‐performing Pt2FeNi/DS‐‐NiFe LDH with a Pt content of 0.98 wt% achieved low overpotential of 204 mV at 10 mA cm−2 and 262 mV at 50 mA cm−2. This work provides a convenient and effective strategy to create additional active sites for enhancing OER performance of NiFe LDH and make contribution to its wide application. [ABSTRACT FROM AUTHOR]

A facile photo-irradiation method is developed to tune active sites over β-Ni(OH)2 nanosheets. Photo-irradiated β-Ni(OH)2 nanosheets possess disordered surface atoms and preferred growth of highly active crystal facets, which exhibit enhanced performance for the electrocatalytic oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

The electronic structure of catalysts influences the electrocatalytic behavior. Herein, the electronic structure of NiO nanocrystals is modified by doping with a small amount of Li+. The Li+ doped NiO nanocrystals show much better OER activity than pristine NiO and LiNiO2, which is a result of tuned Fermi levels, stronger hybridization between Ni 3d and O 2p, and narrowed energy band gap. This work provides a facile strategy to regulate NiO electronic energy bands to promote OER performance. [ABSTRACT FROM AUTHOR]

Because of their low cost and Earth-abundant characteristics, materials based on 3d transition metals have attracted great research interest and are considered as promising electrocatalysts for the oxygen evolution reaction (OER), besides the commercial noble metal-based materials, in recent years. In order to improve electrocatalytic activity, it is necessary to design the structures and compositions of electrocatalysts. In this study, a series of multi-shelled CoxNi1−x oxide/phosphide hollow spheres with tunable element ratios were prepared. The electrocatalytic activity of the multi-shelled CoxNi1−x oxide/phosphide is strongly dependent on the molar ratio of Co and Ni. Based on the combined advantages of complex structures and compositions, the multi-shelled Co0.5Ni0.5 oxide/phosphide displays outstanding electrocatalytic performance in terms of high activity and stable durability for the OER, surpassing those of RuO2 and multi-shelled CoxNi1−x oxide/phosphide with other element ratios of Co and Ni. This result suggests a great possibility of rationally designing the composition for highly efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

Layered metal hydroxides (LMHs) are regarded as a novel and important class of inorganic functional materials. They have unique layered structure and variable chemical compositions that can be readily tuned. In this review, summarized are the recent advances of synthetic routes to the LMHs with designed morphology, composition, and function for electrocatalysis. Versatile products can be readily derived by hybridization, anion‐exchange, surface modification, self‐assembly, etc. More importantly, LMHs can be artificially exfoliated into unilamellar nanosheets with a molecular‐level thickness of about 1 nm versus 2D lateral size in submicrometer or micrometer scale. Molecular‐scale assembly can be then applied to fabricate superlattice‐like composites and functional nanofilms with high quality. The hydroxides can be transformed into oxides, nitrides, or other compounds via different preparation procedures, which can further extend their application prospects. In this regard, the most promising electrocatalysis‐related applications of LMHs and their derivatives are reviewed, such as oxygen evolution reaction, oxygen reduction reaction, hydrogen evolution reaction, CO2 reduction reaction, alcohol or urea electrooxidation, etc. At last, future challenges are also discussed from the aspect of synthesis and application, as well as encouraging advancements are anticipated. [ABSTRACT FROM AUTHOR]

Co3FePx/C nanocomposites were derived from one-step phosphorization of anthraquinone-2-sulfonate (AQS2) intercalated Co3Fe layered double hydroxides (Co3Fe LDHs). The carbonized AQS2 confines Co3FePx nanoparticles in the amorphous carbon matrix during thermal treatment. Ultra-small and uniformly distributed Co3FePx/C nanoparticles in carbon exhibit excellent durability and outstanding OER catalytic activity. [ABSTRACT FROM AUTHOR]

Combining transition metal oxide catalysts with conductive carbonaceous material is a feasible way to improve the conductivity. However, the electrocatalytic performance is usually not distinctly improved because the interfacial resistance between metal oxides and carbon is still large and thereby hinders the charge transport in catalysis. Herein, the conductive interface between poorly conductive NiO nanoparticles and semi‐conductive carbon nitride (CN) is constructed. The NiO/CN exhibits much‐enhanced oxygen evolution reaction (OER) performance than corresponding NiO and CN in electrolytes of KOH solution and phosphate buffer saline, which is also remarkably superior over NiO/C, commercial RuO2, and mostly reported NiO‐based catalysts. X‐ray photoelectron spectroscopy and extended X‐ray absorption fine structure spectrum reveal that a metallic Ni–N bond is formed between NiO and CN. Density functional theory calculations suggest that NiO and CN linked by a Ni–N bond possess a low Gibbs energy for OER intermediate adsorptions, which not only improves the transfer of charge but also promotes the transmission of mass in OER. The metal–nitrogen bonded conductive and highly active interface pervasively exists between CN and other transition metal oxides including Co3O4, CuO, and Fe2O3, making it promising as an inexpensive catalyst for efficient water splitting. [ABSTRACT FROM AUTHOR]

Layered Ni(OH) 2 materials are cheap and efficient electrocatalyst for water splitting. However, pristine Ni(OH) 2 materials usually show poor activity due to the low activity sites and poor conductivity in electrochemical reactions. Herein, layered Ni(OH) 2 nanosheets are grown on the porous Mo 2 N particles for improved interfacial active sites and enhanced conductivity in the oxygen evolution reaction (OER). The OER overpotential of the optimized Mo 2 N/Ni(OH) 2 composite material is distinctly reduced compared with pristine Ni(OH) 2. In addition, the optimized Mo 2 N/Ni(OH) 2 composite material exhibits favorable durability in alkaline electrolyte. Further electrochemical investigation reveals that the Mo 2 N/Ni(OH) 2 composite materials produce increased charge transfer capability and electrochemical active surface area. Theoretical calculation study demonstrates that a redistribution of electron occurred at the interface of Ni(OH) 2 and Mo 2 N, which results in the decrease of energy barrier for the adsorption of OER reactive intermediates at the interfacial atoms. The enhanced performance of OER is thus mainly come from the constructed interface between layered Ni(OH) 2 and porous Mo 2 N. This work gives a feasible method to develop cheap and efficient electrocatalysts for water splitting. [Display omitted] • The Ni(OH) 2 composites with porous Mo 2 N for reduced electrocatalytic OER overpotential and enhanced stability. • The Ni(OH) 2 /Mo 2 N composite materials show distinctly improved electrochemical active areas and conductivity. • DFT calculations reveal the retribution of electrons densities at interface, decreasing the OER energy barrier. [ABSTRACT FROM AUTHOR]

• DFT calculations reveal that Co x Ni 3-x Ge 2 O 5 (OH) 4 catalysts will promote the mass transfer in OER. • The optimized Co 2.4 Ni 0.6 Ge 2 O 5 (OH) 4 shows excellent OER activity in alkaline and neutral electrolytes. • The reduced adsorptive resistance of OER intermediates is the main reason for the enhancement of catalytic performance. • The photovoltaic water splitting by using Co 2.4 Ni 0.6 Ge 2 O 5 (OH) 4 can produce efficiency of solar-to-hydrogen as 4.9 %. It is widely accepted that electronic energy bands of materials seriously affect electrocatalytic performance. However, for transition metal based serpentine materials, the influence of transition metal elements, Ge, and Si on energy bands and subsequently the electrocatalytic OER behavior is not concern yet. Herein, serpentine Co x Ni 3-x Ge 2 O 5 (OH) 4 nanosheets with tuned energy bands are designed for catalyzing OER. DFT calculations reveal that Co x Ni 3-x Ge 2 O 5 (OH) 4 produce intensified density of states around Fermi level in energy bands, bringing feasible absorption of OER intermediates. In experiment, optimized Co x Ni 3-x Ge 2 O 5 (OH) 4 shows low OER overpotential and favorable stability in KOH solution and phosphatic buffer saline, which is superior to commercial RuO 2 and most Co and Ni based compounds. Electrochemical impedance spectra reveal that Co x Ni 3-x Ge 2 O 5 (OH) 4 possesses minimized adsorptive resistance of surface intermediates, which consistent with results of DFT calculations. The serpentine catalysts with tuned energy bands are promising as efficient electrocatalysts for water splitting in wide-pH environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • NiS nanocrystals are anchored on porous Mo 2 N surfaces to construct functional heterointerfaces by forming Mo S bonds. • Mo 2 N/NiS heterointerfaces possess a synergistic effect, which exhibit a much-enhanced activity for overall water splitting. • In a photovoltaic water splitting system, Mo 2 N/NiS achieves a favorable solar-to-hydrogen energy conversion efficiency. Solar-driven electrocatalytic water splitting is a promising technology to produce renewable hydrogen fuel. To accomplish this perspective, it is urgent to exploit high-efficiency and robust bifunctional electrocatalysts. Herein, a hybrid Mo 2 N/NiS heterojunction with synergistic effect is developed as bifunctional electrocatalyst for high-efficiency water splitting in alkaline media. Through high-temperature calcination and in-situ hydrothermal growth process, NiS nanocrystals are successfully anchored on porous Mo 2 N to produce a well-defined heterointerface by forming Mo S bonds. The optimized Mo 2 N/NiS hybrids exhibit a much-enhanced electrocatalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) than that of individual Mo 2 N and NiS in 1.0 M KOH. Moreover, benefitting from the robust chemical stability of Mo 2 N substrate, Mo 2 N/NiS hybrids presents an excellent long-term durability. The density functional theory calculations reveal that the improved HER and OER activities are primarily enabled by the synergistic effect of interface between Mo 2 N and NiS, NiS accelerates the water dissociation while Mo 2 N optimize the intermediates adsorption. When the as-prepared Mo 2 N/NiS heterojunction is used as bifunctional catalysts in a photovoltaic water splitting system, it exhibits a favorable solar-to-hydrogen energy conversion efficiency of 8.4 %, which is superior to some of reported noble-metal based catalysts. This work provides a facile and efficient strategy to design and fabricate the bifunctional catalysts for water splitting. [ABSTRACT FROM AUTHOR]

• Unique NCO@RuO 2 composite nanocones have been constructed. • The heterostructure shows remarkably enhanced overall water splitting performance and stability. • A synergistic effect between NCO and RuO 2 contributes to the enhanced activity. • The involvement of Ru leads to the lattice distortion and oxygen vacancies. • The nanocones possess more oxygen vacancies than nanosheets. Electrocatalytic water splitting is a critical technique for generating clean hydrogen energy, where the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are involved. Generally, the OER process (bottleneck step) occurs more favorably in alkaline solution, while the HER process in acidic solution. Structure or composition design of electrocatalyst are effective strategies to achieve high performances for both OER and HER in alkaline environment toward overall water splitting. Herein, we report a unique electrocatalyst composed of RuO 2 nanoparticles on NiCo 2 O 4 nanocones (NCO@RuO 2 -NCs) hybrid structure via the hydrothermal coprecipitation and subsequent calcination. The NCO@RuO 2 -NCs show higher oxygen vacancy density than that of NiCo 2 O 4 @RuO 2 nanosheets (NCO@RuO 2 -NSs). Employing the NCO@RuO 2 -NCs material as a bifunctional catalyst, a low cell voltage of 1.5 V is capable of overall water splitting with excellent stability of sustaining more than 42 h at 10 mA cm−2 in 1 M KOH electrolyte, which is superior to 2.0 V of NCO@RuO 2 -NSs as well as 1.6 V of commercial Pt/C-RuO 2 couple. The current work may provide a scalable and cost-efficient approach for developing advanced nanocomposite catalysts for water splitting. [ABSTRACT FROM AUTHOR]

The Ni-based metal–organic framework (Ni-MOF) was used as precursor and self-template, and a series of N-doped Ni-Co bimetallic sulfides (N-Ni x Co y -S) were synthesized using oil bath plus solvothermal method. The as-prepared N-Ni x Co y -S displayed hollow sphere structure with a diameter of 300–500 nm. By optimizing the Ni/Co ratio, the precisely tailored N-Ni 1 Co 4 -S material delivered superior oxygen evolution reaction (OER) performances with a small overpotential of 286.2±2.4 mV at 10 mA cm−2. Such the catalyst can further exhibit a long-term catalytic stability with almost no decay during 36h in KOH electrolyte. [Display omitted] • A series of N-doped Ni-Co bimetallic sulfides (N-Ni x Co y -S) were synthesized. • The N-Ni x Co y -S displayed hollow sphere structure with a diameter of 300–500 nm. • The Ni/Co ratio presented a significant impact on electrocatalytic performances. • The N-Ni 1 Co 4 -S showed good catalytic activity with a low overpotential of 286.2 mV. • The N-Ni 1 Co 4 -S exhibited a long-term catalytic stability of 36 h in KOH electrolyte. The development of noble-metal free electrocatalysts with high activity for water splitting is crucial to address the severe energy issue, while the poor conductivity and catalytic stability hinder their commercialization. Traditional heteroatom doping and structural design is still unsatisfactory due to the high cost. Herein, the Ni-based metal–organic framework (Ni-MOF) was used as precursor and self-template, and a series of N-doped Ni-Co bimetallic sulfides (N-Ni x Co y -S) were synthesized using oil bath plus solvothermal method. The as-prepared sulfide displayed hollow sphere structure with a diameter of 300–500 nm. The electrocatalytic activity was investigated using a typical three-electrode system (Hg/HgO and carbon rod as reference electrode and counter electrode, respectively). By optimizing the Ni/Co ratio, the precisely tailored N-Ni 1 Co 4 -S material delivered superior oxygen evolution reaction (OER) performances with a low overpotential of 286.2 ± 2.4 mV at current density of 10 mA cm−2 in 1 M KOH solution (pH = 13.5). Such the catalyst can further exhibit a long-term catalytic stability with almost no decay during 36 h in KOH electrolyte. It demonstrates that this work develops an effective strategy to obtain high-performance and cost-effective electrocatalyst for the water splitting application. [ABSTRACT FROM AUTHOR]

• Facile synthesis of 3D transition-metal core-shell structure electrocatalyst is realized. • Synergy between porous nanosheets and metal nanoparticles rich in defects. • 3D Flower-like transition-metal electrocatalyst exhibit excellent activity for electrocatalysis. The development of high efficiency, low-budget and excellent stability of electrocatalysts is a critical factor to improve water decomposition. Herein, a highly active 3D bulk catalysts of core-shell nanostructures, in which Flower-like CuCoMoOx nanosheets embellished with CoCu alloy nanoparticles are evenly wrapped on Cu NWs cores supported on CF, toward overall water splitting is firstly reported. The coaction of CoCu alloy nanoparticles and CuCoMoOx nanosheets with 3D hierarchical and porous nanoarchitecture can accelerate the ionization of H 2 O molecules and formation of H 2. Meanwhile, the connection nanosheets of Cu NWs with noteworthy conductivity, resulting in rapid electron transport, exhibits outstanding both HER and OER activities and remarkable overall water splitting characteristics in the alkaline medium. As an electrocatalyst for HER and OER, the low overpotential of 75 mV and 315 mV at 100 mA cm−2, and low voltage of 1.66 V for overall water splitting are achieved, even superior to the benchmark of IrO 2 /CF (+) // /Pt/C/CF(-) in 1 M KOH. This work has a significant reference to hydrogen production for the electrolytic water industry. [Display omitted] [ABSTRACT FROM AUTHOR]