Ni-Mo Alloy Electrodeposited over Ni Substrate for HER on Water Electrolysis

Clearing Up Discrepancies in 2D and 3D Nickel Molybdate Hydrate Structures

When electrocatalysts are prepared, modification of the morphology is a common strategy to enhance their electrocatalytic performance. In this work, we have examined and characterized nanorods (3D) and nanosheets (2D) of nickel molybdate hydrates, which previously have been treated as the same material with just a variation in morphology. We thoroughly investigated the materials and report that they contain fundamentally different compounds with different crystal structures, chemical compositions, and chemical stabilities. The 3D nanorod structure exhibits the chemical formula NiMoO4·0.6H2O and crystallizes in a triclinic system, whereas the 2D nanosheet structures can be rationalized with Ni3MoO5-0.5x(OH)x·(2.3 - 0.5x)H2O, with a mixed valence of both Ni and Mo, which enables a layered crystal structure. The difference in structure and composition is supported by X-ray photoelectron spectroscopy, ion beam analysis, thermogravimetric analysis, X-ray diffraction, electron diffraction, infrared spectroscopy, Raman spectroscopy, and magnetic measurements. The previously proposed crystal structure for the nickel molybdate hydrate nanorods from the literature needs to be reconsidered and is here refined by ab initio molecular dynamics on a quantum mechanical level using density functional theory calculations to reproduce the experimental findings. Because the material is frequently studied as an electrocatalyst or catalyst precursor and both structures can appear in the same synthesis, a clear distinction between the two compounds is necessary to assess the underlying structure-to-function relationship and targeted electrocatalytic properties.

Highly efficient Ni-Mo-P composite rare earth elements electrode as electrocatalytic cathode for oil-based drill sludge treatment

It is considered an effective strategy to improve electrochemical performance that introducing rare elements into metal catalysts, which would provide abundant electrochemical active sites and be a benefit for redox reactions. A new Ni-Mo-P composite electrode material modified with rare earth elements (light rare earth Nd and heavy rare earth Yb) was prepared, evaluating the current density of direct current electrodeposition, the doping ratio of Yb and Nd, and the cyclic voltammetry deposition (CVD) cycle numbers on electrode structure and electrochemical performance. The results showed that the electrode has the most obvious amorphous state, the lowest hydrogen evolution overpotential (41.5 mV vs Ag/AgCl) and charge transfer resistance (15.74 Ω/cm²), and remarkable stability when the molar ratio of Yb and Nd was 8:2 and the 20 cycle numbers under the CVD condition. The electrochemical performance and characterization of the electrode showed that there was a good synergistic effect between rare earth elements (Yb, Nd) and Ni-Mo-P alloys. The oil-based drill sludge (OBDS) treatment indicated that the organic matter content is significantly reduced by using the above-modified electrode as the cathode, and the COD and petroleum removal rate can reach up to 85.4 ± 1.2% and 66.2 ± 5.9%. The effect of degradation for aliphatic hydrocarbon was better than aromatic hydrocarbons and no other intermediates are produced during the degradation, which may eventually mineralize the organic matter. This research provided technical support for the preparation of new Ni-Mo-P electrodes modified with rare earth elements and confirmed that electrocatalytic technology was a suitable method for OBDS treatment.

Effect of solution pH, precursor ratio, agitation and temperature on Ni-Mo and Ni-Mo-O electrodeposits from ammonium citrate baths

The induced co-electrodeposition of Ni and Mo is a complex process, where metallic Ni-Mo alloys and Ni-Mo-O composites can originate from the complete and partial reduction of Mo respectively. By adjusting electrolyte compositions and electrodeposition parameters, various metallic, metal/oxide composite, and oxide thin films of Ni-Mo and Ni-Mo-O were electrodeposited from ammonium citrate baths. Ni-ammonia complexes, which play a critical role in promoting the deposition of metallic Ni-Mo alloys, were enhanced at alkaline pH (i.e., 8–10) and lower temperature (i.e., 25–45°C). Moreover, the electrochemical reduction of Ni is under mass transfer limitation, so the deposited Mo content decreased with increasing agitation. On the other hand, higher Mo content can be achieved by relatively higher citrate concentration and larger Mo-to-Ni precursor molar ratio. However, a critical molar ratio of metal precursor resulted in transition from alloy to composite due to Ni inducing the reduction of Mo.

Fabrication of a 3D self-supporting Ni–P/Ni2P/CC composite and its robust hydrogen evolution reaction properties in alkaline solution

The Ni–P/Ni₂P/CC composite exhibits excellent alkaline HER properties derived from Ni–P filling the sites on the CC not occupied by Ni₂P nanosheets.

Pulse electrodeposited nickel with structure directing agents as an electrocatalyst for oxidation of glycerol

Electrodeposition of Ni, Ni–CA and Ni–TBr on mild steel using a pulse technique for electro-oxidation of glycerol.