Formation and Stabilization of NiOOH by Introducing α‐FeOOH in LDH: Composite Electrocatalyst for Oxygen Evolution and Urea Oxidation Reactions

Abstract

well-tuned electronic configuration. [4,5] Especially, with an edge-sharing octahedral MO 6 layer-stacking crystal structure served as highly active sites, NiFe-based layered double hydroxides (NiFe LDHs) exhibited highly remarkable intrinsic electrochemical activity. [6,7] Several studies have reported that NiFe LDH is actually a precatalyst, and it heavily undergoes a self-reconstruction process in basic solution, generating Ni oxyhydroxide (NiOOH) as the active species for OER. [8,9] To begin with, Alexis et al. characterized the vibration mode of NiOOH by in situ Raman spectra, when Ni-Fe films worked as anodes in basic media during the OER. [10] Then, some research revealed that NiOOH species is generally recognized as the positive reaction species and can provide abundant intrinsic catalytic sites for OER. [11][12][13] Not limited to OER, NiOOH can also efficiently catalyze the anodic degradation of urea that featured with the more complex six-electron redox process. [14,15] However, owing to the instability of the high valence state of Ni (III) which can easily transform into Ni (II), the direct synthesis and application of NiOOH have not been realized, unless a high anodic polarization is applied. [16,17] Therefore, it is crucial to explore synthesis methods to stabilize NiOOH catalyst.Among the multiple regulation methods, surface structure reconstruction with the aid of a new phase is widely accepted as a controllable approach for synthesizing novel composites with NiOOH is considered as the most active intermediate during electrochemical oxidation reaction, however, it is hard to directly synthesize due to high oxidation energy. Herein, theoretical calculations predict that α-FeOOH enables a decline in formation energy and an improvement in stabilization of NiOOH in NiFe-based layered double hydroxide (LDH). Inspiringly, a composite composed of α-FeOOH and LDH is well-designed and successfully fabricated in hydrothermal treatment by adding extra Fe 3+ resource, and stable NiOOH is obtained by the following electro-oxidation method. Benefiting from strong electron-capturing capability of α-FeOOH, it efficiently promotes charge redistribution around the Ni/Fe sites and activates Ni atoms of LDH, verified by X-ray photoelectron spectra (XPS) and X-ray absorption spectra (XAS). The d-band center is optimized that balances the absorption and desorption energy, and thus Gibbs free energy barrier is lowered dramatically toward oxygen evolution reaction (OER) and urea oxidation reaction (UOR), and finally showing an outstanding overpotential of 195 mV and a potential of 1.35 V at 10 mA cm −2 , respectively. This study provides a novel strategy to construct highly efficient catalysts via the introduction of a new phase for complex multiple-electron reactions.

AgFe dual cocatalyst for selective conversion of CO2 using K2YTa5O15 photocatalyst

“…Meanwhile, loading the Fe cocatalyst via the sequential photodeposition of Fe and Ag (FeAg/K2YTa5O15) increased both the CO formation rate, which was equal to 63 μmol h −1 (13 times higher than that of the Ag/K2YTa5O15 photocatalyst), and the selectivity towards CO In the case of Fe species, crystallised particles with a lattice spacing of 0.21 nm corresponding to the interplanar spacing of the α-FeOOH structure were observed. [22] According to 35.8 μmol) gradually decreases without irradiation condition, indicating that a small fraction of Fe 3+ ions was adsorbed on the K2YTa5O15 photocatalyst surface, while Fe 2+ ions were not detected at all. In contrast, Fe 3+ ions were rapidly reduced to Fe 2+ ions within 1 min of the photodeposition process, and 99% of Fe 3+ ions was converted to Fe 2+ ions within 120 min of photoirradiation.…”

Vacancy Promotion in Layered Double Hydroxide Electrocatalysts for Improved Oxygen Evolution Reaction Performance

“…The irreversible conversion of Co­(OH) 2 into an amorphous high-valence CoOOH phase is well established in other studies. − However, there is limited understanding about stabilization of the high-valence NiOOH phase after OER processing. Cai et al observed the formation and stabilization of NiOOH in LDH due to the presence of FeOOH and dynamic phase restructuring induced by electrooxidation.…”

Recent advances in direct seawater splitting for producing hydrogen

“…[61][62][63][64] The seawater solution is replaced by the reductive chemical seawater solution as the electrolyte, which are oxidized to high value-added chemicals or CO 2 , or N 2 at the anode. [65][66][67][68] For example, Qiu et al reported an energy-saving hybrid seawater electrolyser using 1 M KOH seawater solution as the catholyte while the 1 M KOH containing 0.5 M hydrazine as the anolyte (Fig. 8(a)-(c)).…”