No abstract

The development of energy storage electrode materials is important for enhancing the electrochemical performance of supercapacitors. Despite extensive research on improving electrochemical performance with polymer-based materials, electrode materials with micro/nanostructures are needed for fast and efficient ion and electron transfer. In this work, highly ordered phosphomolybdate (PMoO)-grafted polyaniline (PMoO-PAI) deposited onto Au hole-cylinder nanopillar arrays is developed for high-performance pseudocapacitors. The three-dimensional nanostructured arrays are easily fabricated by secondary sputtering lithography, which has recently gained attention and features a high resolution of 10 nm, a high aspect ratio greater than 20, excellent uniformity/accuracy/precision, and compatibility with large area substrates. These 10nm scale Au nanostructures with a high aspect ratio of ~30 on Au substrates facilitate efficient ion and electron transfer. The resultant PMoO-PAI electrode exhibits outstanding electrochemical performance, including a high specific capacitance of 114 mF/cm2, a high-rate capability of 88%, and excellent long-term stability.

Humidity sensors provide environmental conditions suitable for several applications. However, they suffer from a limited reliable range originating from the low electrical conductivity and low water-sensitive sites of humidity-sensing materials. In this study, we developed high-sensitivity humidity sensors based on holey-reduced graphene oxide (HRGO) with a large surface area (274.5 m2/g) and an abundant pore structure. HRGO was prepared via the H2O2-etching-reaction-assisted hydrothermal processing of graphene oxide sheets. The resulting humidity sensor exhibited high sensitivity (−0.04317 log Z/%RH, R2 = 0.9717), a fast response time (<3 s), and long-term stability over 28 days. The impedance responses of the humidity sensor were almost similar between the mechanically standard and bent states. Furthermore, electrochemical impedance spectroscopy was performed to understand the humidity-sensing mechanism of the HRGO materials.

A highly sensitive potentiometric pH sensor was developed based on nanopillar array electrodes of iridium oxide. The as‐prepared pH sensor exhibited a high pH sensitivity (69.43 mV/pH), fast response time (8.1 s), and good durability (0.76 mV/h). The sensing performance of the pH sensor was maintained under mechanical bending and even after 1000 repetitive bending/releasing cycles. As a proof‐of‐concept, a wearable headband sensor was fabricated by integrating the pH sensor with a wireless electronic module based on a printed circuit board. The on‐body test indicated that the wearable pH sensor provides reliable and stable data in the real‐time monitoring of pH changes in human sweat during stationary indoor cycling. The pH sensors based on nanopillar array electrodes of iridium oxide have great potential in many portable or wearable applications in healthcare systems, non‐invasive diagnostics, environmental analysis, and food sensors.