NiO–NiMoO₄ Nanocomposites on Multi-Walled Carbon Nanotubes as Efficient Bifunctional Electrocatalysts for Total Water Splitting

Abstract

Multicomponent synergistic regulation and defect design have been effective strategies to enhance the electrocatalytic activity of transition-metal oxides. In this work, NiO and NiMoO 4 nanocomposites on multi-walled carbon nanotubes (termed NiO−NiMoO 4 /mCNTs) are synthesized through a two-step method. Physical characterizations show NiO−NiMoO 4 /mCNTs have a well-defined NiO−NiMoO 4 structure, large specific surface area, and abundant oxygen vacancies. For oxygen evolution reaction (OER), NiO−NiMoO 4 /mCNTs deliver lower overpotential (277 mV) than NiO/mCNTs, NiO, and commercial RuO 2 nanocrystals at 10 mA cm −2 . For hydrogen evolution reaction (HER), NiO−NiMoO 4 /mCNTs still show the best HER activity, manifested by the smallest onset potential and the lowest Tafel. Density functional theory calculations show that the adsorption energies of hydrogen-and oxygen-containing intermediates on the NiO−NiMoO 4 /mCNTs surface have changed, which can lower the energy barriers required for HER and OER. The excellent electrocatalytic activity of bifunctional NiO−NiMoO 4 /mCNTs for OER and HER can be attributed to the synergy effect between NiO, NiMoO 4 , and mCNTs. A symmetrical two-electrode water electrolyzer with NiO− NiMoO 4 /mCNTs as both the cathode and anode are constructed, which can reach a current density of 10 mA cm −2 and only requires 1.57 V.

Enhancing the efficiency of polypyrrole-dodecylbenzene sulfonic acid in-tube solid-phase microextraction coating for analysis of nitrogen-containing pesticides in water environments

“…In terms of coating preparation techniques, this study employed a chemical oxidation method to prepare the PPy-DBSA coating. This method demonstrates better coating uniformity and adhesion compared to traditional physical adsorption or chemical bonding techniques (Wu et al, 2020;Xue et al, 2023). The chemical oxidation method effectively controls the growth of polymer chains, resulting in a more uniform and compact coating (Lee et al, 2021;Bui et al, 2022).…”

Carbon-Based Composites for Oxygen Evolution Reaction Electrocatalysts: Design, Fabrication, and Application

“…[19]. After years of effort, significant progress has been made in the design, preparation, and application of high-performance OER materials, including carbon-based materials (Figure 1) [20][21][22][23]. Efficient nonprecious metal oxides, phosphides, sulfides, and alloys can typically reach a current density of 10 mA cm −2 at an overpotential <300 mV in 1.0 M KOH [20][21][22][23].…”