Hierarchical MoO₄^2– Intercalating α-Co(OH)₂ Nanosheet Assemblies: Green Synthesis and Ultrafast Reconstruction for Boosting Electrochemical Oxygen Evolution

Abstract

Developing highly active oxygen evolution reaction (OER) electrocatalysts is crucial and highly desirable to improve the efficiency of water electrolysis for H2 fuel generation. In this work, hierarchical MoO4 2– intercalating α-Co­(OH)2 nanosheet assemblies were synthesized from the readily available metal source and 2-methylimidazole as the alkaline reagent by green and fast coprecipitation. The ultrathin α-Co­(OH)2-MoO4(25) nanosheets possess a lateral size of about 40–100 nm and a thickness from 2.5 to 4.6 nm (3 to 6 layers). Triggered by OER oxidation treatment, the α-Co­(OH)2-MoO4(25) material undergoes ultrafast and thorough structure reconstruction to CoOOH(25) by only one linear sweep voltammetry scan and chronopotentiometry within 35 s. The in situ transformation leads to the formation of the CoOOH active phase with rich oxygen vacancies and distorted structure, extracting MoO4 2– ions at the same time. Compared with other designed counterparts, CoOOH(25) offers a lower overpotential (309 mV) for the OER at a current density of 10 mA cm–2 and a smaller Tafel slope of only 57.78 mV dec–1, representing an excellent unary CoOOH-based or Co­(OH)2-based catalyst. The improved catalytic activity of CoOOH(25) can be attributed to its specific structures, e.g., ultrathin disordered nanosheets that could facilitate electrolyte transportation and expose more active sites, oxygen vacancies that enhance the intrinsic per-site activity, and their synergistic effect. This established structure self-renewal technology might also be expanded to other advanced nanomaterials toward other electrochemical energy conversion processes.

Boosting the Stability of Oxygen Vacancies in α‐Co(OH)2 Nanosheets with Coordination Polyhedrons as Rivets for High‐Performance Alkaline Hydrogen Evolution Electrocatalyst

“…Similarly, the peaks assigned to α‐Co(OH) 2 in Raman (two peaks at 440 and 487 cm −1 ) and Fourier transform infrared (FTIR, the peaks at 500 and 628 cm −1 corresponding to α‐Co(OH) 2 ; the peaks at 1010, 1195, and 1342 cm −1 corresponding to HMT molecular) spectra (Figure 1g and Figures S6–S7, Supporting Information) decreased gradually and vanished after 300 LSV scans, implying that the α‐Co(OH) 2 nanosheets were completely destroyed and transformed into nanoparticle aggregations with large amount of nanosheets falling off (Figure 1h and Figures S9–S10, Supporting Information). [ 35–37 ] These results suggest that the dissolution and reconstruction of α‐Co(OH) 2 under the strongly alkaline electrolyte were proceeding during HER, and the structure etched by hydroxyl ions finally collapsed, leading to the degradation of the catalytic activity.…”

“…As shown in Figure 2 a, for Co 2p, the two peaks at 781.4 and 797.4 eV can be ascribed to Co 2p 3/2 and Co 2p 1/2 of α‐Co(OH) 2 with two satellite peaks at 786.5 and 803.2 eV. [ 37 ] After the measurements in 1 m KOH, the peak of Co 2p 3/2 at 781.1 eV was negatively shifted by 0.3 eV with a shrunken integration area, suggesting that the electronic structure of Co was significantly changed due to the reduction condition. In contrast, after the addition of MoO 4 2− , the change (−0.15 eV) of the spectrum of Co 2p was efficiently mitigated, and indicatively the electronic structure of Co was better preserved during the alkaline HER.…”

Cobalt-Based Hydrotalcite: A Potential Non-Noble Metal-Based Heterogeneous Catalyst for Selective Hydrogenation of Aromatic Aldehydes

“…The Co 2p spectrum of MgCoMoC shows characteristic signals of Co 2p 3/2 main peaks at 779.8 and 780.6 eV with satellite peaks at 785.5 and 789.3 eV, respectively. Although the main peak positions of cobalt in its +3 and +2 states in an oxygen environment are very close and difficult to distinguish, the presence of two satellite peaks at 789.3 and 785.5 eV confirms the existence of cobalt in both +3 and +2 oxidation states. , This result indicated the formation of a solid solution of cobalt oxide having Co 2+ and Co 3+ ions upon calcination . The Mo 3d XPS spectrum exhibits Mo3d 5/2 and Mo3d 3/2 signals with binding energies of 230.6 and 233.3 eV, respectively.…”

Virtual Special Issue of Recent Research Advances in China: Batteries and Energy Storage

“…Developing energy electrocatalysts to accelerate the hydrogen evolution or oxygen reaction kinetics is critical to facilitate water electrolysis for H 2 generation or achieve high-efficiency metal− air batteries. Meng et al 16 synthesize the ultrathin α-Co(OH) 2 nanosheets intercalated with MoO 4 2− as the oxygen evolution reaction (OER) electrocatalyst. The rapid structural reconstruction triggered by OER leads to the formation of rich active sites and, thus, enhances activity of the materials.…”