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Nanocrystalline Ni-Mo alloy coatings with excellent brightness, high hardness, and corrosion resistance were prepared. Nanocrystalline Ni-Mo alloy coating with a Mo content of 14.94 at% was electrodeposited on the copper foil substrate under the optimized conditions with the current efficiency of 51.64%. The electrodeposition behavior of Ni-Mo alloy coatings was studied by cathodic polarization curve and chronopotentiometry. Chronopotentiometry showed that the nucleation rate of Ni-Mo alloys can be accelerated with the increase of current density. Meanwhile, the cathodic polarization curves show that the additives can effectively inhibit the electrodeposition of Ni-Mo alloys. The (2 0 0) and (2 2 0) diffraction peaks of Ni gradually disappeared and the grain size gradually decreased with the increase of Mo content in the alloy coating according to XRD and TEM analysis. Scanning electron microscope (SEM) and confocal microscope observation results show that the coating becomes smoother and denser with the increase of Mo content when Mo content was lower than 14.94 at%, after which the density of the coating saw a decline due to the intensified hydrogen evolution reaction. The microhardness results of the alloy coating show that the microhardness of the alloy coating is related to the solid solution strengthening, texture evolution, and plastic deformation of the alloy. Meanwhile, the alloy coating has a Hall-Petch relationship and inverse Hall-Petch relationship, and the critical grain size is 5.5 nm. The corrosion resistance of Ni-Mo alloy coating is better than that of pure Ni coating, and the corrosion resistance is optimal when the Mo content is about 15 at%. In addition, in the plating solution containing additives, the deposited Ni-Mo alloy coating is smoother and denser, and the hardness and corrosion resistance of the alloy coating is also greatly improved. [Display omitted] • The minimum grain size of nanocrystalline Ni-Mo alloy coatings can reach 2.7 nm. • The hardness and corrosion resistance of nanocrystalline Ni-Mo alloy coatings are higher than pure Ni coatings. • Composite additives can significantly increase Ni-Mo alloy polarization. [ABSTRACT FROM AUTHOR]

The Zn-air battery is a promising next-generation battery because of the higher energy density and safety compared with the Li-ion battery. However, the Zn-air battery suffers from huge energy loss and poor cycling performance, which are due to the sluggish kinetics of oxygen reduction/evolution reactions (ORR/OER) and the instability of bifunctional catalysts. The state-of-the-art bifunctional catalyst is the composite of Pt and Ir/Ru oxides, which is hindered by the scarce resource and high cost. Therefore, developing low-cost and high-efficient bifunctional non-noble metal-based catalysts is essential to the deployment of Zn-air batteries. Herein, we report a dual-nitrogen-source mediated pyrolysis route to rationally design and synthesize the hybrid Co/Co–N–C bifunctional catalyst. The tailored catalyst consisting of carbon confined Co nanoparticles and atomically dispersed Co–N–C moiety is identified. Remarkably, the dual-nitrogen-source derived Co/Co–N–C catalyst demonstrates excellent electrochemical performances with a half-wave potential of 0.882 V for ORR and a potential of 1.640 V at 10 mA cm−2 for OER; reasonably, the bifunctionality of Co/Co–N–C, which is supported by the excellent self-breathing Zn-air battery performance (the maximum energy density of 897.1 Wh kg Zn −1; no obvious degradation within 167h cycling). The abundant Co-Nx sites and metallic Co nanoparticles synergistically boost the ORR and OER. Image 1 • A dual-nitrogen-source method is proposed to synthesize porous Co-based catalysts. • The dual nitrogen sources play different roles in morphology and structure control. • The hybrid carbon-confined Co nanoparticles and Co-N x sites are well tailored. • The good bifunctionality is due to the hybrid active site configuration. • Excellent performance and lifetime are obtained in a Zn-air battery. [ABSTRACT FROM AUTHOR]

[Display omitted] • Adsorption-coordination mechanism was calculated by quantum chemistry to demonstrate the inhibition effect of MG. • Adsorption-transport mechanism was illustrated to explain the bottom-up growth of cobalt under the influence of MG. • The nucleation and growth of cobalt is 3D diffusion-controlled progressive nucleation process. A novel suppressor, malachite green, was used to achieve bottom-up growth of cobalt in this work. Electrostatic potential, HOMO/LUMO of malachite green was calculated to provide an insight into the interaction between malachite green and metal substrate, while charge distribution, AIM (atoms in molecules theory) analysis and IRI (interaction region indicator) analysis were coupled to analyze the interaction between malachite green and cobalt ions. Adsorption-coordination inhibition mechanism was illustrated to explain the inhibition effect of malachite green. Electrochemical analysis was applied to evaluate malachite green. Cyclic voltammetry was used to confirm the inhibition effect of malachite green, while EQCM analysis demonstrates that the current efficiency was lowered by MG. The nucleation and growth of cobalt is 3D diffusion-controlled progressive nucleation growth under the influence of hydrogen evolution reaction and the compact cobalt coatings could be obtained by surface analysis. The effective MG concentration gradient could be formed within blind vias according to current transient analysis so as to develop electroplating rate difference. The bottom-up growth of cobalt within blind vias was achieved by carrying out electroplating test and the adsorption-transport mechanism was proposed to explain the superconformal electrodeposition of cobalt under the influence of MG. [ABSTRACT FROM AUTHOR]

Rational design and fabrication of high-efficiency electrocatalysts is essential for improving the kinetics of both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), so as to constructing high-performance rechargeable zinc-air batteries (ZABs). Among the promising candidates, transition metal-based (oxy)hydroxides have attracted extensive attention for their considerable catalytic potential on oxygen-involved reaction, while unsatisfactory intermediate adsorption/desorption strength and low conductivity limit their practical feasibility. In this work, interface engineering modification strategy is proposed, and a metal–organic framework derived heterostructure catalyst of CoFeO x H y -CoP@CC is fabricated. Comprehensively analyses demonstrate that the interaction between phosphide-(oxy)hydroxide induces the interfacial electronic redistribution, while the formed Schottky heterostructure facilitates rapid electron transfer. All these kinetically favorable for both OER and ORR, and leads to remarkable bifunctional performance on CoFeO x H y -CoP@CC, with the OER overpotential of 240 mV to deliver the current density of 10 mA·cm−2, which is better than CoP@CC, CC and RuO 2. In practical applications, liquid zinc-air cells assembled by CoFeO x H y -CoP@CC deliver the peak power density up to 117.55 mW cm−2, which is close to that of 20% Pt/C catalyst (108.48 mW cm−2), and considerable operational performance has also been achieved in all solid-state flexible ZABs. • A metal–organic framework derived phosphide-hydroxide heterostructure of CoFeO x H y -CoP@CC was fabricated. • Heterogenous interaction tunes the electronic configuration and facilitates rapid electron transfer, so that enhances electrocatalytic OER and ORR performance. • CoFeO x H y -CoP@CC employed as cathode in both liquid and solid zinc-air cells show considerable operational performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Suppressing effect of NBT on cobalt electrodeposition is confirmed by electrochemical analysis and in situ Raman spectra. • Accelerating effect of NBT on HER is studied by electrochemical methods and finite element simulation. • Suppressing-accelerating effect of NBT is proposed to illustrate the influence of NBT during cobalt electrodeposition. • Nitrotetrazolium blue chloride and convection is of grain refinement during cobalt electrodeposition. Achieving cobalt superconformal (bottom-up) growth is significantly important. Electrochemical methods, including cyclic voltammetry, electrochemical impedance spectra and EQCM-derived Coulomb-voltage curves, were used to confirm the suppressing influence of new suppressor Nitrotetrazolium Blue chloride (NBT). In situ Raman spectroscopy was used confirm that NBT can effectively adsorb on cobalt surface. Besides, EQCM-derived Coulomb-voltage illustrates that it is more beneficial for cobalt electrodeposition at high pH. The NBT effect on hydrogen evolution reaction (HER) was studied by LSV and chronoamperometry. Finite element simulation is used to investigate the accelerating effect of NBT on HER and convection. Suppressing-accelerating effect is proposed to illustrate effect of NBT. NBT can not only suppress the cobalt deposition but also can accelerate local convection by intensifying HER, which can in turn strengthen NBT adsorption. SEM analysis demonstrates that convection and NBT can refine grain. High-quality cobalt is achieved with low SDT values ranging from 24 μm to 45 μm and high FP values (75.4 % for 150 μm, 88.9 % for 100 μm and 87.2 % for 50 μm). [ABSTRACT FROM AUTHOR]

Developing transitional metal-based electrocatalysts with outstanding oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance is essential for energy-efficiency alkaline water electrolysis. Herein, a group of heterostructured electrocatalysts constructing of nickel-based hydroxide (NiX(OH) x , X = Co, Fe) nanosheets decorated on copper phosphide nanowires arrays，were fabricated. Both of the as-prepared NiCo(OH) x -CuP/CF and NiFe(OH) x -CuP/CF present outstanding HER and OER activity, with the overpotential of 79 and 202 mV to deliver 10 mA cm−2, respectively, along with considerable long-term stability. Encouragingly, the NiCo(OH) x -CuP/CF ǀǀ NiFe(OH) x -CuP/CF couple enables sustainable alkaline water electrolysis and powered by a solar-powered system. In-depth analyses elucidate that owing to the modulated heterogeneous interfacial states, both of the catalytic kinetics can be optimized targeting HER and OER, respectively. More significantly, a regulated electrode-electrolyte microenvironment induced by unique arrays nanostructure efficiently promote the electron-mass transfer capacity, thereby facilitating the catalytic activity expression. This work demonstrates the desirable catalytic performance by rationally designing of hydroxide-phosphide heterostructure, and highlights the structural features on catalytic performance promotion. • A delicate NiCo(OH) x -CuP/CF and NiFe(OH) x -CuP/CF catalysts were fabricated, in which the heterogeneous interfacial synergy effect between copper phosphide and nickel-based hydroxide enables the catalytic performance breakthrough. • The modulation of current distribution for the HER and OER optimizing the reaction kinetics, is achieved by interfacial synergy effect between Cu 3 P and nickel-based hydroxide. • The arrays nanostructure features high active area, good electrical conductivity, while also regulate the interfacial microenvironment between electrocatalysts and electrolyte that facilitates electro-mass transfer. [ABSTRACT FROM AUTHOR]