The use of a multiple roughening scheme to enhance sensing performance of pH sensors with NiO nanosheets/multi-walled carbon nanotubes on KOH-etched Si substrates

Sensing electrodes (SEs) fabricated by a multiple surface roughening scheme based on KOH-etched Si substrates with spraying deposited multi-walled carbon nanotubes (MWCNTs) and hydrothermally grown (HTG) NiO nanosheets (NSs) to improve pH sensing performance are demonstrated. A surface area (SA) gain of around 2.31 is obtained from the etched Si substrate, which results in an enhancement in the pH sensitivity of MWCNTs SEs from 52.15 to 54.95 mV pH-1 based on Si substrates without and with KOH etching. Effects of the thermal annealing temperatures and spraying times of the MWCNTs and HTG times of NiO NSs of the proposed NiO NSs/MWCNTs/pyramid-Si SEs on pH sensitivity, hysteresis, and reliability are studied. A near-Nernstian response of 57.56 mV pH-1 is obtained, which could be attributed to the proposed method maximize SA and the number of ion adsorption sites for advancing pH sensing performance.