title: Low-temperature solution processing of palladium/palladium oxide films and their pH sensing performance.
abstract: Highly sensitive, easy-to-fabricate, and low-cost pH sensors with small dimensions are required to monitor human bodily fluids, drinking water quality and chemical/biological processes. In this study, a low-temperature, solution-based process is developed to prepare palladium/palladium oxide (Pd/PdO) thin films for pH sensing. A precursor solution for Pd is spin coated onto pre-cleaned glass substrates and annealed at low temperature to generate Pd and PdO. The percentages of PdO at the surface and in the bulk of the electrodes are correlated to their sensing performance, which was studied by using the X-ray photoelectron spectroscope. Large amounts of PdO introduced by prolonged annealing improve the electrode's sensitivity and long-term stability. Atomic force microscopy study showed that the low-temperature annealing results in a smooth electrode surface, which contributes to a fast response. Nano-voids at the electrode surfaces were observed by scanning electron microscope, indicating a reason for the long-term degradation of the pH sensitivity. Using the optimized annealing parameters of 200°C for 48 h, a linear pH response with sensitivity of 64.71±0.56 mV/pH is obtained for pH between 2 and 12. These electrodes show a response time shorter than 18 s, hysteresis less than 8 mV and stability over 60 days. High reproducibility in the sensing performance is achieved. This low-temperature solution-processed sensing electrode shows the potential for the development of pH sensing systems on flexible substrates over a large area at low cost without using vacuum equipment.
authors.affiliation: Department of Electrical and Computer Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1; Advanced Materials Laboratory, Xerox Research Centre of Canada, 2660 Speakman Drive, Mississauga, ON, Canada L5K 2L1.
authors.forename: Yiheng
authors.initials: Y
authors.lastname: Qin
authors.affiliation: Department of Electrical and Computer Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1.
authors.forename: Arif U
authors.initials: AU
authors.lastname: Alam
authors.affiliation: Department of Chemical Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4L7.
authors.forename: Si
authors.initials: S
authors.lastname: Pan
authors.affiliation: Department of Electrical and Computer Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1. Electronic address: mrhowlader@ece.mcmaster.ca.
authors.forename: Matiar M R
authors.initials: MM
authors.lastname: Howlader
authors.affiliation: Department of Chemical Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4L7.
authors.forename: Raja
authors.initials: R
authors.lastname: Ghosh
authors.affiliation: Department of Mechanical Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4L7.
authors.forename: P Ravi
authors.initials: PR
authors.lastname: Selvaganapathy
authors.affiliation: Advanced Materials Laboratory, Xerox Research Centre of Canada, 2660 Speakman Drive, Mississauga, ON, Canada L5K 2L1. Electronic address: yiliangwu@hotmail.com.
authors.forename: Yiliang
authors.initials: Y
authors.lastname: Wu
authors.affiliation: Department of Electrical and Computer Engineering, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1. Electronic address: jamal@mcmaster.ca.
authors.forename: M Jamal
authors.initials: MJ
authors.lastname: Deen
mesh_terms: D004563:Electrochemistry / Q000295:instrumentation*; D004566:Electrodes; D005898:Glass / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D010165:Palladium / Q000737:chemistry*; D012996:Solutions; D013499:Surface Properties; D013696:Temperature
chemical_list: D012996:Solutions; D010165:Palladium; C048320:palladium oxide
keywords: Low-temperature; PH sensor; Palladium oxide; Potentiometric sensing; Solution processing