Fast response hydrogen gas sensor based on Pd/Cr nanogaps fabricated by a single-step bending deformation

The development of low-cost and high performing hydrogen gas sensors is important across many sectors, including mining, energy and defense using hydrogen (H₂) gas. Herein, we demonstrate a new concept of H₂ sensors based on Pd/Cr nanogaps created by using a simple mechanical bending deformation technique. These nanogap sensors can selectively detect the H₂ gas based on transduction of the volume expansion after H₂ uptake into an electrical signal by palladium-based metal-hydrides that allows closure of nanogaps for electrons flowing or tunneling. While this break-junction architecture, according to literature, can provide several advantages with research gaps in terms of fabricating nanogap sensors with ultra-fast response (≤4 s), the size of nanogap (≤20 nm) and their relationship with time response and recovery as addressed in this paper. Based on the computational modelling outcome, the size of the nanogaps can be investigated in order to optimize the fabrication conditions. Indeed, a single nanogap with optimum width (15 nm) acts as an on-off switch for best performing hydrogen detection. Moreover, with the unique design of Pd/Cr nanogap, the developed sensing device meets major requirement of advanced H₂ gas sensor including room temperature (25 °C) operation, detection of trace amounts (10-40,000 ppm), good linearity, ultra-fast response-recovery time (3/4.5 s) and high selectivity. The presented economical lithography-free fabrication method has simple circuitry, low power consumption, recyclability, and favorable aging properties that promises great potential to be used for many practical applications of H₂ detection.