Metal-organic frameworks (MOFs) have attracted significant research interest for supercapacitor applications due to their high-tunable conductivity and their structure’s pore size. In this work, we report a facile one-step hydrothermal method to synthesize nickel-based metal-organic frameworks (MOF) using organic linker 4,4′-biphenyl dicarboxylic acid (BPDC) for high-performance supercapacitors. The pore size of the Ni-BPDC-MOF nanostructure is tuned through different synthesization temperatures. Among them, the sample synthesized at 180 °C exhibits a nanoplate morphology with a specific surface area of 311.99 m²·g⁻¹, a pore size distribution of 1–40 nm and an average diameter of ~29.2 nm. A high specific capacitance of 488 F·g⁻¹ has been obtained at a current density of 1.0 A·g⁻¹ in a 3 M KOH aqueous electrolyte. The electrode shows reliable cycling stability, with 85% retention after 2000 cycles. The hydrothermal process Ni-BPDC-MOF may provide a simple and efficient method to synthesize high-performance hybrid MOF composites for future electrochemical energy storage applications.

Hierarchical three-dimensional (3D) flower-like n-ZnO/p-NiO heterostructures with various Zn_xNi_y molar ratios (Zn₅Ni₁, Zn₂Ni₁, Zn₁Ni₁, Zn₁Ni₂ and Zn₁Ni₅) were synthesized by a facile hydrothermal method. Their crystal phase, surface morphology, elemental composition and chemical state were comprehensively investigated by XRD, SEM, EDS, TEM and XPS techniques. Gas sensing measurements were conducted on all the as-developed Zn_xNi_y-based sensors toward ammonia (NH₃) detection under various working temperatures from 160 to 340 °C. In particular, the as-prepared Zn₁Ni₂ sensor exhibited superior NH₃ sensing performance under optimum working temperature (280 °C) including high response (25 toward 100 ppm), fast response/recovery time (16 s/7 s), low detection limit (50 ppb), good selectivity and long-term stability. The enhanced NH₃ sensing capabilities of Zn₁Ni₂ sensor could be attributed to both the specific hierarchical structure which facilitates the adsorption of NH₃ molecules and produces much more contact sites, and the improved gas response characteristics of p-n heterojunctions. The obtained results clear demonstrated that the optimum n-ZnO/p-NiO heterostructure is indeed very promising sensing material toward NH₃ detection for different applications.

Flexible electrode is crucial for wearable electronic devices. To prevent performance degradation due to bending or stretching, the development of highly flexible and durable materials is imperative. Here, we address this challenge by selecting stainless-steel electrodes with excellent stability and flexibility. Through an anodization process on the stainless steel, we created an integrated flexible iron oxide electrode. Chemical vapor deposition and ion implantation were employed to develop concentration-controllable N-doped iron oxide electrodes. Comparative analysis highlights the outstanding performance of ion-implanted electrodes, with a specific capacitance increase of up to 3.01 times (332.375 mF cm−2) at 1 mA cm−2. The N-doped electrode exhibits a capacitance retention of 76.67% after 8000 cycles. Density functional theory calculations reveal N-induced lattice distortion, enhancing ion transport and reducing the bandgap. Leveraging these insights, a flexible asymmetric supercapacitor is assembled, demonstrating exceptional stability and capacitance characteristics across different voltages. The flexibility of the stainless-steel substrate enables the FSC to maintain capacitive performance during bending. This research presents a promising solution for high-performance and stable capacitors in electrochemical energy storage applications.