Rational assembly and hetero-growth of hybrid structures consisting of multiple components with distinctive features are a promising and challenging strategy to develop materials for energy storage applications. Herein, we propose a supercapacitor electrode comprising a three-dimensional self-supported hierarchical MnCo-layered double hydroxides@Ni(OH)₂ [MnCo-LDH@Ni(OH)₂] core–shell heterostructure on conductive nickel foam. The resultant MnCo-LDH@Ni(OH)₂ structure exhibited a high specific capacitance of 2320 F g⁻¹ at a current density of 3 A g⁻¹, and a capacitance of 1308 F g⁻¹ was maintained at a high current density of 30 A g⁻¹ with a superior long cycle lifetime. Moreover, an asymmetric supercapacitor was successfully assembled using MnCo-LDH@Ni(OH)₂ as the positive electrode and activated carbon (AC) as the negative electrode. The optimized MnCo-LDH@Ni(OH)₂//AC device with a voltage of 1.5 V delivered a maximum energy density of 47.9 W h kg⁻¹ at a power density of 750.7 W kg⁻¹. The energy density remained at 9.8 W h kg⁻¹ at a power density of 5020.5 W kg⁻¹ with excellent cycle stability.

Cation substitution is a promising strategy for modulating the structural properties and optimizing the electrochemical performance of spinel cobalt oxide (Co₃O₄); however, the underlying mechanism of this action induced by different cation substitutions has not yet been clearly addressed.

With the increasing demands of indoor air quality monitoring, highly sensitive and selective gas sensor arrays consisting of metal oxide semiconductors have been increasingly studied. As an effective strategy to obtain the desired performance, noble metal functionalization is frequently chosen owing to its target-specific sensing mechanisms. However, the lack of a comprehensive analysis on the sensing mechanisms of different combinations of metal oxides and noble metals limit the versatility of these sensor arrays for use in selective gas sensor arrays. In this study, we fabricate a 3 × 3 gas sensor array to obtain a reliable comparison of the sensing mechanism through the use of three metal oxides—WO₃, SnO₂ and NiO—in three different nanostructure forms: a thin film and dome-like nanostructures with and without Au nanoparticle (NP) decoration. The responses of the sensor arrays to four target gases (CH₃COCH₃, C₆H₅CH₃, NH₃, and H₂S) are generally enhanced by the dome-like nanostructure and show distinctively enhanced responses when the sensors are decorated with Au NPs. Moreover, the dome-like SnO₂ with Au NPs shows an increase of up to 121 times for C₆H₅CH₃ compared with the pristine SnO₂ thin film. Additionally, the sensitization effects of Au NPs depend on the types of metal oxides and gases, which improve the gas discrimination capability by diversifying the gas selectivity of the sensor units in the array. The prepared sensor array can distinguish four target gases by principal component analysis (PCA). The contributions of different enhancement mechanisms, which are dependent on the gases and metal oxides, are investigated by comparing the activation energy of each gas response with and without Au. The comparison among the chosen gases reveals that the decoration of Au NPs is effective for C₆H₅CH₃ and NH₃ regardless of the type of metal oxide. Among the metal oxides, the effects of Au NPs on gas responses are in the order of SnO₂, NiO, and WO₃, in which the energy level difference between the Au NPs and metal oxide are 0.2, 0.1, and −0.6 eV, respectively. These results confirm that the dominant enhancement mechanism of Au NPs for each combination of gases and metal oxide is a decrease in activation energy. Therefore, this study provides a systematic understanding of the sensitization mechanism of Au NPs on metal oxides toward gases for the fabrication of selective gas sensor arrays.