Cunying Xu

Facile electrochemical preparation of self-supported porous Ni–Mo alloy microsphere films as efficient bifunctional electrocatalysts for water splitting

The exploration of low-cost, stable, and robust electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is urgently needed for developing renewable-energy storage and conversion techniques. In this study, we report a facile one-step electrodeposition route to prepare self-supported porous Ni–Mo alloy microsphere (Ni–Mo MS) films directly grown on copper foils from a deep eutectic solvent, ethaline (mixture of choline chloride and ethylene glycol), as a highly efficient and durable catalyst for both the HER and OER in 1.0 M KOH. The prepared Ni–Mo MS/Cu, as a hydrogen-evolving cathode, shows remarkable catalytic performance toward the HER with a small Tafel slope of 49 mV dec−1 and a low HER overpotential of −63 mV to deliver 20 mA cm−2. Serving as an oxygen-evolving anode, the catalyst also offers excellent OER catalytic activity with a moderate Tafel slope of 108 mV dec−1, and reaches 20 mA cm−2 at an OER overpotential of 335 mV. Utilized as both the cathode and anode in a symmetric two-electrode water electrolysis system, the bifunctional catalyst requires a cell voltage of 1.59 V to reach an overall water splitting current density of 10 mA cm−2 with robust durability, which could be potentially used in water splitting devices for practical applications.

Synthesis of micro-FeTi powders by direct electrochemical reduction of ilmenite in CaCl2-NaCl molten salt

Micro-ferrotitanium powders have been prepared by molten salt electrolysis via directly electrochemical reduction of solid ilmenite in eutectic CaCl2-NaCl melt at 973 K. In the direct electrochemical reduction process, the reduction of FeTiO3 first gives rise to the formation of Fe and CaTiO3, which as intermediates will be further deoxidized at the interface of iron metals, solid CaTiO3 matrix, and electrolyte to directly form ferrotitanium alloy powders in porous structure. Furthering the electrolytic time can promote the dense structure of ilmenite pellet turn to be more porous, indicating pores inside the pellet are sufficient for the diffusion of oxygen ions. Based on the reduction behavior of partially reduced powders in metallic cavity electrode during the cathodic potentiostatic electrolysis, it shows that the slow deoxidization rate is mainly caused by the more and more difficult reduction of CaTiO3 than that of FeTiO3.

Facile electrodeposition of cauliflower-like S-doped nickel microsphere films as highly active catalysts for electrochemical hydrogen evolution

The development of low-cost, earth-abundant, and high-efficiency catalysts for electrocatalytic water splitting is central to developing sustainable and clean energy. The abundant reserves of nickel sulfides are promising noble metal-free materials for the hydrogen evolution reaction (HER). In this work, a highly active cauliflower-like S-doped nickel microsphere film directly grown on a copper wire (CW) substrate (labeled as NiSx/CW) was facilely prepared via a one-step electrodeposition approach in a choline chloride/ethylene glycol (ethaline)-based deep eutectic solvent. Doping of S is found to induce an interesting structural transition from nanosheets to porous cauliflower-like microspheres, electronic structure changes at the surface, and a significant improvement in the HER catalytic performance. The as-prepared NiS0.25/CW with a Ni/S atomic ratio of 1 : 0.25 exhibits the best performance, showing a negligible onset potential (−18 mV) with a low overpotential (−54 mV at 10 mA cm−2) and small Tafel slope (54 mV dec−1) in 1.0 M KOH solution. Additionally, the NiS0.25/CW catalyst displays good durability and affords long-term electrolysis without activity degradation for 60 h. This study offers a facile synthesis route for in situ growth of the active phases on current collectors to fabricate self-supported noble-metal free HER catalysts and deep insights into the relationships among the S-doping, catalyst microstructure, and catalytic properties.

Engineering nanoporous Ag/Pd core/shell interfaces with ultrathin Pt doping for efficient hydrogen evolution reaction over a wide pH range

The rational design and fabrication of highly efficient and durable all-pH catalysts for sustainable electrochemical hydrogen production are of critical importance to building renewable energy systems for the future. By employing an in situ electrochemical alloying/dealloying generated nanoporous Ag (NPA) as the supporting substrate, we propose a facile galvanic replacement reaction (GRR) synthesis route in a deep eutectic solvent (Ethaline), combined with an electrochemical activation process to fabricate monolithic 3D nanoporous Ag/Pd core/shell hybrids with ultrathin (sub 1 nm) amorphous Pt-rich skin (Pt–Pd@NPA), showing excellent hydrogen evolution reaction (HER) catalytic performance and durability over a wide pH range. The optimized Pt–Pd@NPA requires low overpotentials of −28.1, −34.8, and −23.8 mV to drive a catalytic current density of −10 mA cm−2 with small Tafel slopes of 31.2, 32.2, and 32.5 mV dec−1 in acidic (0.5 M H2SO4), neutral (1.0 M PBS), and alkaline (1.0 M KOH) media, respectively, which outperforms most previously reported noble-metal-based HER electrocatalysts. Impressively, this hybrid catalyst is capable of steadily delivering a fairly large current density of 1000 mA cm−2 in highly acidic media (0.5–7.0 M H2SO4), promising its practical use in advanced water-splitting devices. The superior HER performance is ascribed to the 3D interconnected nanoporous architectures and synergies between the Ag–Pd skeletons and active Pt. Theoretical calculations confirm that the electronic structure of the Ag–Pd hybrids is optimized by the incorporation of Pt, which results in optimal hydrogen adsorption free energy on the surface and leads to significantly enhanced HER activity and durability. Our work offers a new idea for the design and fabrication of advanced high-performance electrocatalysts for the HER over a wide range of pH values.

The Effect of Water on the Tin Electrodeposition from [Bmim]HSO4 Ionic Liquid

The electrodeposition of tin from SnO in ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO4) in the presence of water at different cathodic potential was investigated. With the addition of water to [Bmim]HSO4 ionic liquid, the electrochemical window of the electrolyte decreases and the reduction potential of Sn(II) positively shifts. The water content of ionic liquid electrolyte has a distinct effect on morphology of the deposits. As water content increased from 0 to 50% (v/v), the morphology of deposits varies from granular to hexagonal rod-like, then to hollow tubular, and finally to wire-like. The XRD phase analysis showed that both Sn and CuSn alloys were deposited in ionic liquid/water mixtures. However, in dried ionic liquids only Cu3Sn was obtained, surprisingly. The difference in the structure might be attributed to the various interactions of the ions with the Cu substrate. In addition, the deposition potential was found to play a significant role in the morphology of deposits.