The hollow PtPdRhRuCoNi high-entropy alloy was synthesized via an oil-bath and subsequent etching. With a specific surface area 1.7 times larger than Pt black, it exhibits superior activity and stability in 1 M KOH electrolytes containing ethanol, ethylene glycol, or glycerol. These improvements originate from the synergistic effect between its unique hollow architecture, which provides abundant accessible active sites, and its multi-element composition, which optimizes the electronic structure and facilitates efficient electron transfer.

In this work, we introduce hierarchical heterophosphide interface catalysis (HHIC) for water splitting. 3D self-supported hollow columnar FeP4-Ni5P2-NiMoP2 arrays is synthesized via hydrothermal synthesis, ion exchange, and controlled phosphidation. The hollow columnar architecture integrates three phosphide phases, creating abundant heterogeneous interfaces that enlarge active surface area. In 1.0 M KOH, it requires only 238 mV to achieve a current density of 100 mA cm-2 for the OER, outperforming commercial RuO2. The over-potential for the HER is 145 mV at 100 mA cm-2, surpassing commercial Pt/C. DFT calculations reveal optimal hydrogen binding (0.03 eV) and reduced OER energy barrier (1.81 eV), clarifying the HHIC mechanism. The assembled symmetric electrolyzer operated at a cell voltage of only 1.68 V and maintained 95% activity over 100-h continuous operation at 100 mA cm-2 for water splitting. This work shows an effective strategy to fabricate bifunctional low-cost catalysts for water electrolysis.

The development of highly active and cost-effective electrocatalysts is essential for advancing the hydrogen evolution reaction (HER) in water splitting. Herein, Ni@PtIrRhCo nanodendrites (NDs) were synthesized through a simple oil bath method. These NDs exhibit a dendritic structure assembled from branched nanocrystals. Benefiting from their multielement composition and structural features, the catalysts demonstrate superior HER activity under both alkaline and acidic conditions. Specifically, in 1.0 M KOH and 0.5 M H2SO4, the overpotentials required to reach 10 mA cm−2 are merely 24 mV and 51 mV, respectively, outperforming those of previously reported electrocatalysts. Moreover, the Ni@PtIrRhCo NDs exhibit outstanding catalytic stability during prolonged operation. This study offers a straightforward yet effective route toward the development of advanced HER electrocatalysts with both high activity and robust stability.

The dual-site synergistic catalytic mechanism on NiFeOOH suggests weak adsorption of Ni sites and strong adsorption of Fe sites limited its activity toward alkaline oxygen evolution reaction (OER). Large-scale density functional theory (DFT) calculations confirm that Co doping can increase Ni adsorption, while the metal vacancy can reduce Fe adsorption. The combined two factors can further modulate the atomic environment and optimize the free energy toward oxygen-containing intermediates, thus enhancing the OER activity. Accordingly, we used Co doping and Cr vacancies to fabricate an amorphous catalyst of VCr,Co-NiFeOOH. It provides an OER overpotential of 239 mV at 100 mA cm-2 and high stability over 500 h at 500 mA cm-2 with a ∼98% potential retention. The resulting water electrolyzer based on an anion exchange membrane (AEM) exhibits a remarkable performance of 1 A cm-2 at 1.68 V in 1 M KOH. XPS, soft-XAS, and XANES combined with Bader charge analysis results reveal that the regulation of the local microenvironment can increase the valence state of Ni by Co doping, thus improving the adsorption energy on Ni sites. The Cr vacancy can alleviate the strong adsorption on Fe sites. DFT calculations confirm that the synergistic effect of Co doping and Cr vacancies can redistribute the charge on the Ni/Fe sites, optimize the d-band center of Ni and Fe, and endow the catalyst with Ni-Fe dual sites to reduce the energy barrier of the OER rate-determining step.

Density functional theory (DFT) calculations demonstrate neighboring Pt atoms can enhance the metal activity of NiCoP for hydrogen evolution reaction (HER). However, it remains a great challenge to link Pt and NiCoP. Herein, we introduced curvature of bowl-like structure to construct Pt/NiCoP interface by adding a minimal 1 ‰-molar-ratio Pt. The as-prepared sample only requires an overpotential of 26.5 and 181.6 mV to accordingly achieve the current density of 10 and 500 mA cm −2 in 1 M KOH. The water dissociation energy barrier ( E a ) has a ~43 % decrease compared with NiCoP counterpart. It also shows an ultrahigh stability with a small degradation rate of 10.6 μV h −1 at harsh conditions (500 mA cm −2 and 50 °C) after 3000 hrs. X-ray photoelectron spectroscopy (XPS), soft X-ray absorption spectroscopy (sXAS), and X-ray absorption fine structure (XAFS) verify the interface electron transfer lowers the valence state of Co/Ni and activates them. DFT calculations also confirm the catalytic transition step of NiCoP can change from Heyrovsky (2.71 eV) to Tafel step (0.51 eV) in the neighborhood of Pt, in accord with the result of the improved H ads at the interface disclosed by in situ electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) tests.

Exposing more catalytic active sites is an effective strategy to enhance the catalyst activity for hydrogen evolution reaction (HER). Herein, Ti3C2Tx MXene served as a substrate to load thin and curved 2H-MoSe2 nanosheets by a typical hydrothermal method, forming MoSe2/MXene heterointerface with the fully exposed Mo edge sites. And then, atomically dispersed Ru single atoms (RuSAs) were successfully anchored on the MoSe2/MXene (RuSAs@MoSe2-MXene). The X-ray absorption near edge structure (XANES) demonstrates that Ru is loaded as single atoms on MoSe2 and MXene. The prepared sample exhibits improved catalytic activity with a small overpotential of 49 mV at 10 mA cm-2 and a low Tafel slope of 52 mV dec- 1 for HER in 0.5 M H2SO4. It also exhibits excellent stability with a small attenuation voltage of 10 mV for 120 h at 10 mA cm-2 in 0.5 M H2SO4. When assembled into a two-electrode system of RuSAs@MoSe2-MXene||RuO2, it only requires a relatively low potential of 1.626 V at 10 mA cm-2 to drive overall water splitting (OWS). Control experiments disclose the highly improved performance can be primarily attributed to the introduced RuSAs and MoSe2/MXene heterointerfaces exposing more active sites of Ru and Mo. Moreover, the high conductivity of MXene can increase charge transfer in HER process. The interface engineering with multiple interfaces can provide fresh impetus for the development of efficient HER catalysts.

Four-electron process and the interference of Cl- make sluggish kinetics on oxygen evolution reaction (OER) for seawater electrolysis. Herein, NiFe LDH grown on NiFe-foam with CeO2 modification and (W2O7)(2-)intercalation was synthesized by one-step hydrothermal method. It only needs 353.8 and 386.7 mV to achieve a large current density of 1000 mA center dot cm(-2) in 1 M KOH and alkaline natural seawater, respectively. The catalytic material can stand 100 h with a retention of 98.1% at 1000 mA center dot cm(-2) in alkaline natural seawater. Experiments and theo-retical calculations confirm that the state-of-the-art OER activity comes from the introduced CeO2 with optimized adsorption energy of intermediates. The improved stability and selectivity in seawater can be ascribed to the preferential adsorption of Ni and Fe with higher valence on OH- based on hard and soft acid based (HSAB) principle by (W2O7)(2-)intercalation. This work provides a viable approach to develop efficient catalytic material for large-current seawater electrolysis.

Hydrogen energy, a green renewable energy, has shown great potential in developing new energy and alleviating environmental problems. Water electrolysis is an effective method to achieve large-scale clean hydrogen production, but this process needs to consume a huge amount of electric energy. It is urgent to develop high-activity, high-stability and low-cost catalysts to reduce the consumption of electric energy. At present, the noble metal catalyst is the star material in the hydrogen evolution reaction (HER), but its stability and high cost restrict its large-scale application. In this review, we comprehensively discussed the research progress on noble metal-based heterogeneous electrocatalysts used in water electrolysis for hydrogen production. Firstly, we analyzed the influence factors for hydrogen production performance, including the mass transfer process, the adsorption–desorption process, the catalytic process, and the influence of the working electrode and electrolyte. Then, we discussed the relationship between catalytic activity and electronic structure and chemical composition in view of theoretical calculations and summarized the strategies for developing efficient catalysts (alloying and interface engineering). Finally, we highlighted the challenges for the practical application of noble metal-based hydrogen evolution electrocatalysts.

To develop quick‐charge sodium‐ion battery, it is significant to optimize insertion‐type anode to afford fast Na + diffusion rate and excellent electron conductivity. First‐principles calculations reveal the TiO subcompound superiority for Na + diffusion following Ti(II)O > Ti(III)O > Ti(IV)O. Hence, in situ growth of amorphous TiO subcompounds with rich oxygen defects based on Ti 3 C 2 T x ‐MXene is developed. Meanwhile, the composite presents expanded MXene interlayer spacing and much enhanced conductivity. The synergistic effect of enhanced electron/ion conduction gives a high capacity of 107 mAh g −1 at 50 A g −1 , which gives 50% and 150% increasements compared with one counterpart without valence adjustment and another one without MXene expansion. It only needs 20 s (at 30 A g −1 ) to complete the discharge/charge process and obtains a capacity of 144.5 mAh g −1 , which also shows a long‐term cycling stability at quick‐charge mode (121 mAh g −1 after 10000 cycles at 10 A g −1 ). The enhanced performance comes from fast electron transfer among TiO subcompounds contributed by rich‐defect amorphous TiO 2–x , and a reversible change of elastic MXene with interlayer spacing between 1.4 and 1.9 nm during Na + insertion/extraction process. This study provides a feasible route to boost the kinetics and develop quick‐charge sodium‐ion battery.

A challenging task is to promote Ru atom economy and simultaneously alleviate Ru dissolution during the hydrogen evolution reaction (HER) process. Herein, Ru nanograins (≈1.7 nm in size) uniformly grown on 1 T ‐MoS 2 lace‐decorated Ti 3 C 2 T x MXene sheets (Ru@1 T ‐MoS 2 ‐MXene) are successfully synthesized with three types of interfaces (Ru/MoS 2 , Ru/MXene, and MoS 2 /MXene). It gives high mass activity of 0.79 mA µg Ru −1 at an overpotential of 100 mV, which is ≈36 times that of Ru NPs. It also has a much smaller Ru dissolution rate (9 ng h −1 ), accounting for 22% of the rate for Ru NPs. Electrochemical tests, scanning electrochemical microscopy measurements combined with DFT calculations disclose the role of triple interface optimization in improved activity and stability. First, 2D MoS 2 and MXene can well disperse and stabilize Ru grains, giving larger electrochemical active area. Then, Ru/MoS 2 interfaces weakening H * adsorption energy and Ru/MXene interfaces enhancing electrical conductivity, can efficiently improve the activity. Next, MoS 2 /MXene interfaces can protect MXene sheet edges from oxidation and keep 1 T ‐MoS 2 phase stability during the long‐term catalytic process. Meanwhile, Ru@1 T ‐MoS 2 ‐MXene also displays superior activity and stability in neutral and alkaline media. This work provides a multiple‐interface optimization route to develop high‐efficiency and durable pH‐universal Ru‐based HER electrocatalysts.

Heterointerfaces can adjust the adsorption energy with intermediates in the transition state for a much decreased kinetics energy barrier (Ea). One typical transition metal phosphide, NiCoP grains (∼5 nm in size), was anchored on a Ti3C2Tx MXene monolayer (∼1 nm in thickness) to boost the kinetics toward alkaline hydrogen evolution reaction (HER). General electrochemical experiments at different temperatures give a small Ea of 31.4 kJ mol-1, showing a 22.1% decrease compared to its counterpart NiCoP nanoparticles (40.3 kJ mol-1). Impressively, the overpotential of NiCoP@MXene dramatically decreases from 71 mV to 4 mV at 10 mA cm-2 when the temperature increases from 25 °C to 65 °C. On a single NiCoP@MXene sheet, scanning electrochemical microscopy (SECM) tests also give a very close value of Ea = 31.9 kJ mol-1, with a relative error of ∼1.6%. Density functional theory (DFT) calculations confirm the interface between NiCoP and MXene can effectively decrease the energy barrier of water dissociation by 16.0%. The three kinds of studies on macro, micro/nano, and atomic scales disclose the interfaces can reduce the kinetics energy barrier about 16.0-22.1%. Besides, the photothermal effect of MXenes can easily raise the catalyst temperature under vis-NIR light, which has been applied in practical scenarios under sunlight for energy savings.

Numerous studies have been focused on renewable energy conversion devices (e.g. fuel cell and Zn-air battery) to mitigate the climate changing and serious environmental degradation. Herein, hydrogel derived FeCo/FeCoP embedded in N, P-doped three-dimensional porous carbon framework (FeCo/FeCoP@NP-CF) was prepared by the high-temperature pyrolysis and subsequent acid-etching. Polyacrylamide (PAM) would absorb water here to form hydrogel and act as the C and N sources, which is conducive to capture and in-situ reduce metal ions. The hybrid porous carbon framework had interconnection, highly open structures and molecular accessible hierarchical surfaces. The resultant FeCo/FeCoP@NP-CF displayed remarkable oxygen reduction reaction (ORR) characteristics with a more positive half-wave potential (E-1/2) of 0.85 V in 0.1 M KOH electrolyte, surpassing commercial Pt/C (E-1/2 = 0.84 V). This work offers some valuable guidelines for synthesis of non-noble metal catalysts in energy technologies.

The design of low-cost and efficient electrocatalysts is critical for oxygen evolution reaction (OER) to overcome the high overpotential and sluggish kinetics. Herein, a new non-precious metal electrocatalyst by synergistically coupling spindle-like Fe3N hollow nanorods with Ni2Co layered double hydroxides (Fe3N@Ni2Co-LDHs) was fabricated via annealing spindle-like Fe2O3 hollow nanorods in NH3 atmosphere, followed by refluxing in oil bath in the existence of Co(NO3)(2)center dot 6H(2)O, Ni(NO3)(2)center dot 6H(2)O, urea and polyvinylpyrrolidone (PVP). Impressively, the Fe3N@Ni2Co-LDHs nanohybrids with heterointerfaces shows remarkable OER performance with extremely low overpotential (only 240 mV to achieve a current density of 10 mA cm(-2)) and small Tafel slope (38.9 mV dec(-1)) for OER in alkaline medium. The enhanced OER performance could be attributed to the strong interfacial interaction between Fe3N and Ni2Co-LDHs, and improved electrical conductivity of the nanohybrids. This work might provide a feasible route for the development of efficient electrocatalysts with hetero-interfaces in renewable energy system. (C) 2020 Elsevier B.V. All rights reserved.

Exploring hydrogen evolution reaction (HER) catalyst with highly catalytic features in alkaline conditions is considered as significance for water splitting. In this study, a general and simple method was developed to prepare flower-like platinum-cobalt-ruthenium alloy nanoassemblies (PtCoRu NAs) by using murexide and cetyltrimethylammonium chloride (CTAC) as the co-structure-directing agents. Benefiting from the structural advantages and multimetallic compositions, the as-prepared PtCoRu NAs displayed remarkably enhanced electrocatalytic performance for the HER in 1.0 M KOH, with a low overpotential (eta, 22 mV) to drive 10 mA cm(-2), small Tafel slope (46 mV dec(-1)), and high exchange current density (j(0), 3.30 mA cm(-2)) during the long-term electrolysis. The as-developed strategy sheds some valuable guidelines for preparing advanced multimetallic catalysts for production of hydrogen in fuel cells. (C) 2019 Elsevier Inc. All rights reserved.

Controllable synthesis of low-cost, highly effective and operationally durable multifunctional electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is crucial for enhancing the efficiency of water splitting and metal-air batteries. Herein, well-defined bimetallic CoFe alloyed nanocrystals wrapped in nitrogen-doped graphitic carbon nanocubes (CoFe@N-GCNCs-700) are synthesized by pyrolysis of CoFe-based Prussian blue analogue nanocubes@phenolic resin. The resulting CoFe@N-GCNCs-700, as an advanced trifunctional catalyst, exhibits prominent electrocatalytic behaviors for ORR (0.802 V of half-wave potential), OER (273 mV of overpotential at 10 mA cm-2) and HER (91.5 mV of overpotential at 10 mA cm-2) in the alkaline solution. Furthermore, its practicability is further exploited by overall water splitting. The output voltage of only 1.63 V is demanded to achieve a current density of 10 mA cm-2. Besides, the CoFe@N-GCNCs-700 based rechargeable Zn-air batteries exhibit large peak power density (132.5 mW cm-2) and superior cycling stability (100 h without evident degeneration). This research offers some new prospects in fabrication of highly effective multifunctional catalysts for electrochemical energy applications.

Exploring efficient, cost-effectiveness and stable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical for rechargeable metal-air batteries. Herein, CoFe alloyed nanocrystals encapsulated in N, P-codoped carbon nanovesicles assembled hollow spheres (CoFe@NP-CHS) are prepared by pyrolyzing the homogenous mixture of vitamin B12 (VB12), melamine and Fe2O3 at 700 degrees C. The resultant CoFe@NP-CHS demonstrates distinct activity for ORR and OER in the alkaline media. More impressively, the as-developed Zn-air battery displays excellent performance with enhanced open-circuit voltage of 1.516 V, enlarged peak power density of 123.1 mW cm(-2), and remarkable cycling stability at 10 mA cm(-2) (40 h), outperforming the mixture of commercial Pt/C + RuO2 catalysts. This work provides a promising avenue to fabricate efficient, low cost and stable electrocatalyst for practical viability in electrochemical energy devices.

Alkaline hydrogen evolution reaction (HER) electrocatalysts with high catalytic activity and long-term durability are of significance for sustainable energy applications. Herein, we prepared trimetallic PtNiCo hollow alloyed 3D multipods (HAMPs) with rough surfaces by an effective one-pot solvothermal strategy coupled with acid etching, as evidenced by a series of characterizations. By virtue of the trimetals and unique structures, the PtNiCo HAMPs exhibited excellent HER performance in 1.0 M KOH electrolyte with a low overpotential (eta, 20 mV) and small Tafel slope (46.3 mV dec(-1)), superior to homemade PtNi HAMPs, PtCo nanocrystals (NCs) and commercial Pt/C catalysts. This study provides some constructive guidelines for synthesis of advanced hollow multimetallic catalysts in energy systems. (C) 2020 Elsevier Inc. All rights reserved.

Developing efficient and stable electrocatalysts with three-dimensional (3D) hierarchical nanostructures is extremely important in practical applications of direct alcohol fuel cells. Herein, 3D hierarchical thornlike multi-metallic PtPdNiCu alloyed nanotripods (PtPdNiCu TNTPs) were efficiently fabricated by a one-pot aqueous method, in which Pluronic F127 performed as the structure-director and dispersing agent. The as-prepared PtPdNiCu TNTPs exhibited distinct electrocatalytic activity for methanol oxidation reaction (MOR) with a mass activity (MA) of 1.465 A mg(Pd)(-1), which is superior to commercial Pt/C (0.925 A mg(Pd)(-1)) in 1.0 M KOH solution, along with the greater MA (1.019 A mg(Pd)(-1)) for ethanol oxidation reaction (EOR) than Pt/C (0.712 A mg(Pd)(-1)). This work would provide an impetus for rationally constructing multimetal nanomaterials to commercial implementation of advanced alcohol fuel cells. (C) 2020 Elsevier Inc. All rights reserved.

Hierarchically branched multi-metallic nanoassembles are promising catalysts extensively used in catalytic fields because of their unique structural features and multicompositions advantages. Herein, three-dimensional (3D) hierarchical zigzag-branched urchin-like PdCuPt superstructures (HZBUS) were prepared by a one-pot wet-chemical method, where polyethylene oxide (PEO) and KBr served as directing agents. The specific architectures provided abundant active sites highly available for reactants, in turn showing highly enlarged electrochemically active surface area (16.79 m(2)g(Pd)(-1)). The as-obtained PdCuPt HZBUS displayed dramatically enhanced catalytic activity and improved long-term durability for formic acid oxidation reaction (FAOR), surpassing homemade PdCu nanoparticles (NPs), commercial Pd black and PVC catalysts. This work offers a new strategy for construction of advanced multimetallic electrocatalysts with charming superstructures and high-efficient performances in fuel cells.