Electrodeposited Zn-Ni alloys as promising catalysts for hydrogen production-Preparation, characterization and electro-catalytic activity

Unique hierarchical NiFe-LDH/Ni/NiCo2S4 heterostructure arrays on nickel foam for the improvement of overall water splitting activity

The development of environmentally friendly, high-efficiency, stable, earth-abundant and non-precious metal-based electrocatalysts with fast kinetics and low overpotential for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of exceeding significance but still challenging. Herein, a bifunctional electrode of unique hierarchical NiFe-LDH/Ni/NiCo2S4/NF (NiFe-LDH = nickel-iron layered double hydroxide and NF = nickel foam) electrocatalytic architecture, which is built up from NiFe-LDH nanosheets, Ni nanoparticles and NiCo2S4 nanoneedles sequentially arrayed on a porous NF substrate, has been prepared by a facile hydrothermal and electrodeposition method. This electrocatalytic architecture is binder-free and its outer NiFe-LDH nanosheets can effectively prevent the oxidation of inner Ni nanoparticles and corrosion of NiCo2S4 nanoneedles during water electrolysis. The integration of effective HER Ni nanoparticles into OER NiFe-LDH and NiCo2S4 electrocatalysts can not only overcome the disadvantage of their poor electrical conductivity, but also greatly improve their HER and OER activities, owing to the unique hierarchical heterostructure and multicomponent synergies among Ni, NiFe-LDH, and NiCo2S4. Consequently, this electrode shows better OER performance with ultra-low overpotential of 192 mV at 10 mA cm-2, a small Tafel slope of only 37 mV dec-1 and high stability in comparison with commercial RuO2, and also exhibits excellent HER activity with a low overpotential of 83 mV at 10 mA cm-2. More importantly, the NiFe-LDH/Ni/NiCo2S4/NF composite serves as anode and cathode for overall water splitting, and it requires a low cell potential of only 1.53 V to reach a current density of 10 mA cm-2, which evidently exceeds that of the standard Pt-C/NF//RuO2/NF cell of 1.61 V. This work provides a feasible strategy to prepare high-efficiency, low-cost and non-precious metal-based electrocatalysts for overall water splitting.

In Situ Reconstructed Zn doped Fex Ni(1- x ) OOH Catalyst for Efficient and Ultrastable Oxygen Evolution Reaction at High Current Densities

Developing FeOOH as a robust electrocatalyst for high output oxygen evolution reaction (OER) remains challenging due to its low conductivity and dissolvability in alkaline conditions. Herein, it is demonstrated that the robust and high output Zn doped NiOOH-FeOOH (Zn-Fe_x Ni_(1-x) )OOH catalyst can be derived by electro-oxidation-induced reconstruction from the pre-electrocatalyst of Zn modified Ni metal/FeOOH film supported by nickel foam (NF). In situ Raman and ex situ characterizations elucidate that the pre-electrocatalyst undergoes dynamic reconstruction occurring on both the catalyst surface and underneath metal support during the OER process. That involves the Fe dissolution-redeposition and the merge of Zn doped FeOOH with in situ generated NiOOH from NF support and NiZn alloy nanoparticles. Benefiting from the Zn doping and the covalence interaction of FeOOH-NiOOH, the reconstructed electrode shows superior corrosion resistance, and enhanced catalytic activity as well as bonding force at the catalyst-support interface. Together with the feature of superaerophobic surface, the reconstructed electrode only requires an overpotential of 330 mV at a high-current-density of 1000 mA cm^-2 and maintains 97% of its initial activity after 1000 h. This work provides an in-depth understanding of electrocatalyst reconstruction during the OER process, which facilitates the design of high-performance OER catalysts.

Flower-like Ni3Sn2@Ni3S2 with core-shell nanostructure as electrode material for supercapacitors with high rate and capacitance

To enhance the specific capacitance as well as maintain satisfactory rate performance of nickel hydroxide and nickel sulfide, in this work, the ultra-fine nickel-tin nanoparticles with high conductivity are selected to synthesize Ni₃Sn₂@Ni(OH)₂ and Ni₃Sn₂@Ni₃S₂ nanoflowers. Alloy as the core material improves the electrical conductivity of the composite, and the nanosheets prepared by electrochemical corrosion effectively avoid aggregation as well as increase the active sites of the electrode material. By adjusting the corrosion time, the Ni₃Sn₂@Ni(OH)₂ with better morphology displays a high specific capacitance (1277.37C g^-1 at 1 A g^-1) and good rate performance (1028C g^-1 at 20 A g^-1). After sulfurization, the optimal Ni₃Sn₂@Ni₃S₂ perfectly retains the morphological characterizations of the precursor and exhibits ultra-high specific capacitance (1619.02C g^-1 at 1 A g^-1) as well as outstanding rate performance (1312C g^-1 at 20 A g^-1). The samples before and after vulcanization both have the excellent electrochemical properties, which is attributed to the rational design and construction of the alloy-based core-shell nanostructures. Besides, the all-solid-state hybrid supercapacitor (HSC) is assembled by Ni₃Sn₂@Ni₃S₂ as the positive electrode and activated carbon as the negative electrode, displaying outstanding energy density of 70.54 Wh kg^-1 at 808.67 W kg^-1 and excellent cycling stability (93.21 % after 10,000 cycles). This work provides a novel ingenuity for synthesizing high-performance supercapacitor electrodes.

Design of SnO2:Ni,Ir Nanoparticulate Photoelectrodes for Efficient Photoelectrochemical Water Splitting

Currently, hydrogen generation via photocatalytic water splitting using semiconductors is regarded as a simple environmental solution to energy challenges. This paper discusses the effects of the doping of noble metals, Ir (3.0 at.%) and Ni (1.5-4.5 at.%), on the structure, morphology, optical properties, and photoelectrochemical performance of sol-gel-produced SnO2 thin films. The incorporation of Ir and Ni influences the position of the peaks and the lattice characteristics of the tetragonal polycrystalline SnO2 films. The films have a homogeneous, compact, and crack-free nanoparticulate morphology. As the doping level is increased, the grain size shrinks, and the films have a high proclivity for forming Sn-OH bonds. The optical bandgap of the un-doped film is 3.5 eV, which fluctuates depending on the doping elements and their ratios to 2.7 eV for the 3.0% Ni-doped SnO2:Ir Photoelectrochemical (PEC) electrode. This electrode produces the highest photocurrent density (Jph = 46.38 mA/cm2) and PEC hydrogen production rate (52.22 mmol h-1cm-2 at -1V), with an Incident-Photon-to-Current Efficiency (IPCE% )of 17.43% at 307 nm. The applied bias photon-to-current efficiency (ABPE) of this electrode is 1.038% at -0.839 V, with an offset of 0.391% at 0 V and 307 nm. These are the highest reported values for SnO2-based PEC catalysts. The electrolyte type influences the Jph values of photoelectrodes in the order Jph(HCl) > Jph(NaOH) > Jph(Na2SO4). After 12 runs of reusability at -1 V, the optimized photoelectrode shows high stability and retains about 94.95% of its initial PEC performance, with a corrosion rate of 5.46 nm/year. This research provides a novel doping technique for the development of a highly active SnO2-based photoelectrocatalyst for solar light-driven hydrogen fuel generation.

Bifunctional nanoporous Ni-Zn electrocatalysts with super-aerophobic surface for high-performance hydrazine-assisted hydrogen production

In the present study, an effective approach is proposed to replace the oxygen evolution reaction with the substituted anodic hydrazine oxidation reaction (HzOR) to assist in hydrogen generation based on a bifunctional porous Ni-Zn electrocatalyst with nanosheet arrays. The Ni-Zn catalyst exhibits an extraordinary HzOR performance with a high current density of 970 mA cm^-2 at 0.7 V, and 93.8% of its initial activity after 5000 s, simultaneously delivering an overpotential of 68 mV at 10 mA cm^-2 for the hydrogen evolution reaction. Moreover, the electrolytic cell is constructed employing Ni-Zn catalysts as both the anode and cathode, achieving 100 mA cm^-2 at an ultralow cell voltage of 0.497 V with an outstanding stability over 10 h. The superior electrocatalytic performance can be ascribed to its porous structure with large active surface area, high electrical conductivity, and most importantly the super-aerophobic nature of the Ni-Zn surface. This work also provides a novel approach to designing and constructing porous structured non-noble metal bifunctional electrocatalysts with super-aerophobic surface to be used for energy-saving hydrogen production.

Spectroscopic properties and activated mechanism of NO on isolated cationic tantalum clusters: A first-principles study

The adsorption and dissociation of NO on the cationic Ta₁₅⁺ cluster were investigated using the density-functional theory (DFT) calculations, and the Ta-centered bicapped hexagonal antiprism (BHA) structure of cationic Ta₁₅⁺ cluster can be identified as the global minimum, which reproduces well the infrared multiple photo dissociation (IR-MPD) spectrum. Our results show that the cationic BHATa₁₅⁺ cluster provides the hollow region for NO to interact effectively, and possess larger adsorption strength on the region than other sites. The density of states, charge density differences and frontier molecular orbitals were analyzed to understand the electronic properties of the stable NO-adsorbed isomers. The characteristic IR peaks of the firstly two low-lying isomers are properly assigned, in which the strongest IR peak originates from the N - O stretching vibration. For the dissociation of NO on the BHATa₁₅⁺ cluster, it is found that the reaction path II easily occurs rather than path I due to small reaction barrier, and the cluster may possess the great catalytic behavior to dissociate NO molecule. The present results will inevitably stimulate future theoretical and experimental studies for the design of novel Ta-based catalytic materials for the NO dissociation.

Cyclic voltammetry growth and characterization of Sn–Ag alloys of different nanomorphologies and compositions for efficient hydrogen evolution in alkaline solutions

Electrodeposition of silver, tin and their alloys from different aqueous electrolytes suffer from various environmental issues and deposits are affected by H₂ evolution and metal oxide formation.