Synergistic Engineering of Doping and Vacancy in Ni(OH)₂ to Boost Urea Electrooxidation

Abstract

Nickel hydroxide (Ni(OH)2) has been identified as one of the best promising electrocatalyst candidates for urea oxidation reaction (UOR) due to its flexible structures, wide compositions, and abundant 3d electrons under alkaline conditions. However, its layered structure with limited exposed edge sites severely hinders further improvement of the UOR activity. Herein, oxygen‐vacancy rich and vanadium doped Ni(OH)2 (Ovac‐V‐Ni(OH)2) catalysts are prepared and synergistically boost the urea electrooxidation. Vanadium doping contributes more exposed active sites, and simultaneously generates oxygen vacancies, switching the rate‐determining step of UOR from *COOH deprotonation to the N–H bond cleavage process and lowering the thermodynamic barrier by around 1.13 eV. The novel Ovac‐V‐Ni(OH)2 demonstrates good electrocatalytic performances with a working potential of 1.47 V at a high current density of 100 mA cm−2. Synergistic engineering of doping and oxygen vacancy is a promising strategy for designing efficient UOR electrocatalysts.

Fabrication of Ni/NiFe-LDH Core–Shell Schottky Heterojunction as Ultrastable Bifunctional Electrocatalyst for Ampere-Level Current Density Water Splitting

“…Impressively, the obtained solar energy-to-hydrogen conversion device maintained desirable water splitting stability for 30 days (Figure 4d) with a large and variable current density input and a stable hydrogen yield of 1500 mL day −1 (Figure S22). 45 In addition, the XPS spectra obtained after the HER stability tests were very similar to the initial spectra, while both the Fe 2p and Ni 2p peaks exhibited positive shifts of 0.7 and 0.44 eV after OER, respectively. These results suggest that Ni/NiFe-LDH was oxidized during the OER process, which is consistent with the observed catalyst morphology after OER.…”

“…The overall morphology and XRD spectrum of Ni/NiFe-LDH/IF remained almost unchanged after stability testing. Several tiny flakes grew on the catalyst surface during OER mostly because of the formation of NiOOH species caused by recombination of the Ni layer. − Moreover, the Raman spectrum of the catalyst significantly changed after HER and initial, which confirmed the presence of NiOOH by detecting the Ni III –O bending and stretching vibrations . In addition, the XPS spectra obtained after the HER stability tests were very similar to the initial spectra, while both the Fe 2p and Ni 2p peaks exhibited positive shifts of 0.7 and 0.44 eV after OER, respectively.…”

Electrocatalytic urea oxidation: advances in mechanistic insights, nanocatalyst design, and applications

“…Recently, Jiao et al synthesized V-doped Ni(OH) 2 with abundant oxygen defects using a hydrothermal technique. 104 As shown in Fig. 9h and i, the electrons in the d orbital of the metal were redistributed by introducing oxygen defects, which results in the rate-limiting step of urea oxidation shifting from deprotonation to the N–H bond cleavage step.…”

Ni-Doped MnO2 Nanosheet Arrays for Efficient Urea Oxidation

“…Among all the reported UOR electrocatalysts in alkaline solutions, Ni-based materials (alloys, hydroxides, oxides, sulfides, nitrides, phosphides, etc.) have been most widely investigated, due to their intrinsic high activities, and relatively low costs. − In general, Ni-based catalysts are first electrochemically oxidized to form NiOOH species on the surface, and then the as-generated NiOOH is regarded as a catalytically active site for urea oxidation, which can well explain the fact that the onset potential of UOR is quite close to the potential where NiOOH forms in many previously reported Ni-based catalysts. − However, since NiOOH appears at high potentials of 1.35–1.4 V vs RHE, a large overpotential of about 1.0 V is generally required for UOR on most Ni-based catalysts, which greatly increases the energy consumption of UOR-related electrolysis systems . Recently, Chen and co-workers successfully prepared Ni 2 Fe­(CN) 6 with extremely high UOR activities .…”