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The precise design and development of high-performing oxygen evolution reaction (OER) for the production of industrial hydrogen gas through water electrolysis has been a widely studied topic. A profound understanding of the nature of electrocatalytic processes reveals that Ni-based catalysts are highly active toward OER that can stably operate at a high current density for a long period of time. Given the current gap between research and applications in industrial water electrolysis, we have completed a systematic review by constructively discussing the recent progress of Ni-based catalysts for electrocatalytic OER at a large current density, with special focus on the morphology and composition regulation of Ni-based electrocatalysts for achieving extraordinary OER performance. This review will facilitate future research toward rationally designing next-generation OER electrocatalysts that can meet industrial demands, thereby promoting new sustainable solutions for energy shortage and environment issues. [ABSTRACT FROM AUTHOR]

Reasonable design of Pd-based catalysts with specific composition and morphology is of great importance for promoting the commercial application. of direct alcohol fuel cells (DAFCs). Recently, two-dimension (2D) with high density of defects and massive low-coordinated surface atom has become research highlights in the field of catalysis. Herein, we report a wet chemical method for synthesizing PdCu nanosheets with abundant wrinkles. The ultrathin two-dimensional structure endows catalysts plentiful catalytic active sites and large specific surface area, improving atomic utilization efficiency. The formation of bimetallic PdCu alloy structure leads to the adjustment of Pd electronic structure, resulting in lattice compression effect. Benefitting from the structural and compositional characteristics, PdCu nanosheets (NSs) exhibits excellent electrocatalytic performance for ethylene glycol oxidation reaction (EGOR) and glycerol oxidation reaction (GOR) with the mass activity of 7031 mA mg−1/5117 mA mg−1, which is 4.4/3.9 times higher than that of commercial Pd/C catalysts. Furthermore, the remained mass activity of PdCu NSs is 3991/3851 mA mg−1 after the durability measurement for EGOR/GOR, which confirm PdCu NSs possesses superior stability. We believe that our synthetic strategy could provide robust reference for the development of high-performance eletrocatalysts. [Display omitted] • PdCu nanosheets were prepared by a facile solvothermal method. • The PdCu NSs provide ideal electrocatalytic active sites. • The PdCu NSs exhibited excellent electrocatalytic performance toward EGOR and GOR. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal organic frameworks (MOFs) are considered as promising electrocatalytic materials due to their tunable porosity, functional organic ligands, and large specific surface area for oxygen evolution reaction (OER). Recently, most reported electrocatalysts focus on the establishing heterogeneous structures by thermal treatments to improve OER performance. However, the thermal treatments are accompanied by the complex synthetic process and destruction of the MOFs structure. Therefore, improving the catalytic performance of pristine MOFs remains a challenge. Here, a series of trimetallic M a M b M c -MOFs (M represents metal element) were synthesized by one-pot method. Modulating the Co/Ni ratio not only adjusts the morphology of FeCoNi-MOFs, but also effectively optimizes the electronic structure. The composition-optimized FeCo 0.5 Ni 2.5 -MOF nano-bundles (FeCo 0.5 Ni 2.5 -NBs) only required a low overpotential of 273 mV to achieve the current density of 10 mA cm−2 in alkaline solution, with a Tafel slope of 51.1 mV dec−1, lower than other FeCoNi-MOFs and commercial RuO 2 catalyst. The two-electrode couple FeCo 0.5 Ni 2.5 -NBs || Pt/C achieved the cell voltage of 1.55 V, delivering current density of 10 mA cm−2 for overall water splitting. [ABSTRACT FROM AUTHOR]

Fe@CoMo 2 S 4 /Ni 3 S 2 /NF catalysts with enhanced conductivity, enlarged electochemical active areas and modulated electronic structure for efficient water splitting. [Display omitted] Oxygen evolution reaction (OER) is a multi-electron transfer process, whose intrinsic sluggish dynamic restricts the whole process of overall water splitting (OWS). To address this issue, a porous transition metal sulfide (TMS) catalyst with rich heterojunctions was prepared by vulcanization and trace Fe doping of CoMo-based metal–organic framework (MOF). In this work, the nanoflower composed of ultrathin 2D nanosheets anchored on a nickel foam presents a layered interface that contributes to the exposure of active regions. The resulting electrode denoted as Fe@CoMo 2 S 4 /Ni 3 S 2 /NF required a low overpotential (η 10 = 167 mV @ 10 mA cm−2, η 50 = 260 mV @ 50 mA cm−2) in 1.0 M KOH for OER and a small cell voltage (E = 1.513 V @ 10 mA cm−2) to power OWS when coupled with commercial Pt/C. It also exhibited splendid morphological and chemical stability with virtually invariant polarization curve and flower-like appearance after 1000 CV cycles, as well as long-term durability over 100 h with a constant current density of 10 mA cm−2. This work revealed the multi-anionic regulation mechanism in the surface reconstruction of sulfide electrocatalysts, and verified that Co/Mo/Ni-based oxysulfide was the true active substance of OER, which inspired the understanding and design of multi-anionic regulated electrocatalysts. [ABSTRACT FROM AUTHOR]

A sequential template-engaged method was applied to design and construct unique Pt-NiCoFeP@NiCoFe-PBA hollow nanocages. Impressively, constructing heterointerfaces and incorporating ultralow Pt could induce strong synergistic effects and modify electronic configurations to optimize the binding energy of intermediates, thus achieving prominent electrocatalytic performance. [Display omitted] • Exploiting a partial phosphidation strategy to ingeniously construct heterostructures. • Ultralow Pt-loading to regulate electronic structure and increase active sites of catalysts. • Three-dimensional cage-like nanostructure could promote efficient charge transfer. • Pt-NiCoFeP@NiCoFe-PBA exhibits admirable electrocatalytic activity toward OER. Developing highly efficient electrocatalysts based on appropriate heterojunction engineering and electronic structure modification for the oxygen evolution reaction (OER) has been extensively recognized as an effective approach to increase the efficiency of water splitting. Herein, ultralow Pt-loaded (1 %) NiCoFeP@NiCoFe-PBA hollow nanocages with well-defined heterointerfaces and modified electronic environment are successfully fabricated. As expected, the obtained Pt-NiCoFeP@NiCoFe-PBA exhibits outstanding performance with a low overpotential of 255 mV at 10 mA cm−2 and a small Tafel slope of 57.2 mV dec-1. More specifically, the highly open three-dimensional structure, exquisite interior voids and abundant surface defects endow Pt-NiCoFeP@NiCoFe-PBA nanocages with more electrochemical active sites. Meanwhile, experimental results and mechanism studies also reveal that the construction of heterogeneous interfaces as well as incorporation of noble metals could readily induce strong synergistic effects and significantly tailor electronic configurations to optimize the binding energy of the intermediates, thereby achieving prominent OER performance. [ABSTRACT FROM AUTHOR]

Ru-modified NiFe MOF nanosheet array was elaborately designed via self-driven galvanic replacement reaction (GRR), which exhibits dramatically enhanced HER, OER and UOR catalytic property as a multifunctional electrocatalyst. [Display omitted] • Ru-modified NiFe MOF nanosheet array was designed via self-driven galvanic replacement reaction. • Enhanced catalytic potency benefitted from spontaneous electronic reconstruction in the interface. • The Ru-NiFe- x /NF are endowed with richer high-valence Ni active species. • The Ru-NiFe- x /NF can operate as multifunctional electrocatalyst with high current density. Urea electro-oxidation reaction (UOR) has been a promising strategy to replace oxygen evolution reaction (OER) by urea-mediated water splitting for hydrogen production. Naturally, rational design of high-efficiency and multifunctional electrocatalyst towards UOR and hydrogen evolution reaction (HER) is of vital significance, but still a grand challenge. Herein, an innovative 3D Ru-modified NiFe metal-organic framework (MOF) nanoflake array on Ni foam (Ru-NiFe- x /NF) was elaborately designed via spontaneous galvanic replacement reaction (GRR). Notably, the adsorption capability of intermediate species (H*) of catalyst is significantly optimized by Ru modification. Meanwhile, rich high-valence Ni active species can be acquired by self-driven electronic reconstruction in the interface, then dramatically accelerating the electrolysis of water and urea. Remarkably, the optimized Ru-NiFe-③/NF (1.6 at% of Ru) only requires the overpotential of 90 and 310 mV to attain 100 mA cm−2 toward HER and OER in alkaline electrolyte, respectively. Impressively, an ultralow voltage of 1.47 V is required for Ru-NiFe-③/NF to deliver a current density of 100 mA cm−2 in urea-assisted electrolysis cell with superior stability, which is 190 mV lower than that of Pt/C-NF||RuO 2 /NF couple. This work is desired to explore a facile way to exploit environmentally-friendly energy by coupling hydrogen evolution with urea-rich sewage disposal. [ABSTRACT FROM AUTHOR]

A series of CoNi-based CoNiM (M= Fe, Cd, Ce, Cu, Mn, Zn) LTHs nanocatalysts with ultrathin nanosheet configuration are prepared as efficient electrocatalysts for OER. [Display omitted] • We developed a simple MOF-mediated method for synthetizing ultrathin 2D CoNiFe LTHs. • The modified electronic structure leads to high OER activity of the CoNiFe LTHs. • This work will boost the synthesis of ternary layer hydroxide catalysts. Developing low-budget, stable, and high-performance electrocatalyst toward oxygen evolution reaction (OER) is of pivotal significance in the fields of energy conversion and storage. Herein, a universal metal organic framework (MOF)-mediated method for the synthesis of two-dimensional (2D) layered triple hydroxides (LTHs) nanosheets with ultrathin nature has been developed. It is interesting to disclose that the CoNi-based LTHs possess better electrochemical catalytic performance, giving superior performance to commercial RuO 2 catalysts. Remarkably, benefitting from the ultrathin nanosheet configuration, optimized electronic structure, and strong synergistic effect, the optimized CoNiFe LTHs nanosheets show excellent OER performance with an ultralow overpotential of 262 mV at a current density of 10 mA cm−2 and a small Tafel slope of 88.1 mV dec-1. This work provides a promising avenue to develop low-cost and high-performance layered ternary hydroxide electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of open-structured amorphous/crystalline CoNiRuO x heterointerface nanocages are prepared by a simple method. • The suitable crystallinity and defects levels could be simultaneously precise regulated. • The optimized CoNiRuO x -2 PNCs exhibited the superior OER activity with an overpotential of 245 mV at 10 mA cm−2. Amorphous/crystalline (a/c) metal-oxide nanocages with defects are promising materials towards the realization of efficient water electrocatalysis. In this work, we not only constructed a Ru doping porous nanocages (PNCs) structure, but also studied the relationship between both crystallinity of a/c degrees and oxygen vacancy (O vac) levels in a/c CoNiRuO x PNCs catalysts and their catalytic properties. Owing to the rich mass transfer channels, optimized crystallinity and O vac levels, and efficient catalytic model of "Ni-O-Co-O-Ru-O-Ni" for well-distributed electron density, the optimized CoNiRuO x -2 PNCs exhibited the alkaline oxygen evolution reaction (OER) properties with an overpotential of 245 mV at 10 mA cm−2 and remarkable stability for 60 h, surpassing other series of a/c CoNiRuO x and benchmark RuO 2 catalysts. In addition, the electrode couple a/c CoNiRuO x -2//Pt/C only need an ultralow voltage of 1.54 V to drive overall water splitting. This work proposed the introduction and quantitative control on both a/c heterostructure degree and O vac level, offering guidelines for OER catalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amorphization/crystallization methods of TM-based catalysts are summarized. • Various kinds of a/c TM-based catalysts are reviewed. • Perspectives and challenges of a/c TM-based catalysts for water splitting are outlined. The rational phase engineering on transition-metal-based (TM-based) catalysts is an efficient strategy to improve the catalytic performance for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in water splitting. Combining high conductivity from crystalline phase with orderly atomic arrangement and high activity from amorphous phase with abundant unsaturated sites, more amorphous/crystalline (a/c) heterostructure TM-based catalysts with optimized electronic structures have been confirmed to exhibit superior OER and HER properties with well-balanced activity and stability. However, the rational design of the a/c TM-based catalysts for water splitting is often ignored. In this review, we firstly summarized the amorphization/crystallization strategies for constructing a/c TM-based catalysts including pyrolysis method, composition-tuned approach, electrochemical method, chemical etching and other strategies. Then, we introduced various kinds of a/c TM-based catalysts such as a/c TM-based alloys, oxides and hydroxides, nitrides/phosphides/sulfides, and composites. In addition, the roles of a/c interfaces on the performance promotion for OER and HER have been analyzed, which involved the active sites increasement with optimized d-band center, catalytic kinetics acceleration with fast electron transfer, and stability enhancement with electron density redistribution. Finally, we proposed the existing challenges and further perspectives referring to the precise synthesis, in-depth activity investigation and performance promotion. [ABSTRACT FROM AUTHOR]

[Display omitted] • The MOF-derived CoNiFeP nanospindles catalysts are prepared by a facile ion-exchange and phosphorization method. • The CoNiFeP with unique yolk-shell structure exhibit rich channels for mass transportation. • The construction of robust phosphide heterojunction interface in CoNiFeP boost the electron transfer. • The promotion mechanism of OER property is analyzed on CoNiFeP with well-tuned composition. The heterogeneous interface engineering of nanocatalysts has been proved as an efficient strategy to promote the oxygen evolution reaction (OER) catalytic performance. Different from the conventional hollow structures, the yolk-shell construction could defend the distortion and dissolution during OER for stability improvement. However, it is still a great challenging to simultaneously construct heterogeneous interface and yolk-shell structure based on electrocatalysts with well-tuned composition and structure. Herein, we developed a facile synthetic method to prepare the yolk-shell trimetallic phosphide catalysts by starting with MIL-88A nanospindles templates. Benefitting from heterogeneous interface with fast electron transfer, yolk-shell architecture with rich channels for mass transportation, and active metal doping with electron structure modulation, the obtained CoNiFeP yolk-shell nanospindles (YSNSs) catalysts displayed superior OER catalytic properties with the overpotential of only 261 mV to deliver a current density of 10 mA cm−2 in alkaline media. Furthermore, the yolk-shell architecture endowed CoNiFeP with remarkable OER stability for 60 h. By coupling CoNiFeP with Pt/C electrodes to drive overall water splitting, an ultralow cell voltage of 1.56 V is required. The experimental and mechanistic studies indicated the optimized binding energy of *OOH ad and *OH ad intermediates by constructing robust phosphide interface. [ABSTRACT FROM AUTHOR]

[Display omitted] • A MOF mediated method has been proposed for the synthesis of (Ru-Co)O x nanobox. • The (Ru-Co)O x nanoboxes are endowed with rich vacancies and interfaces. • The doping of ultralow Ru effectively modifies the electronic structure of CoO x. • (Ru-Co)O x nanoboxes could deliver outstanding electrocatalytic OER performance. For accelerating the reaction kinetics of oxygen evolution reaction (OER) and improving the efficiency of water electrolysis, it is essential to develop high-performance and robust OER electrocatalysts. Herein, heterostructured ruthenium-cobalt oxide hollow nanoboxes are developed for enabling a highly efficient OER electrocatalysis. Benefitting from the desirable structural and compositional merits of more exposure of surface active centers, modulated electronic structure, and interfacial synergy effect, the (Ru-Co)O x hollow nanobox could exhibit excellent electrocatalytic performance toward OER. Particularly, an extremely low overpotential of 265 mV is necessary for the optimized (Ru-Co)O x -350 to achieve a current density of 10 mA cm−2, together with a small Tafel slope of 60 mV dec-1. More interestingly, by combing (Ru-Co)O x -350 with Pt/C for driving alkaline water splitting, an ultralow cell voltage of merely 1.57 V is required. [ABSTRACT FROM AUTHOR]