Fabrication of High-Performance pH Sensor Based on NiO/Mxene/PANI Modified Sensing Platform
Authors: Yelmai Syda Wasy , Alom Nur , Han Tan Kim , Saidur R , Jamal Mamun 
Published: February 2024

Accurate pH measurement is a fundamental cornerstone in various scientific and industrial processes, playing a pivotal role in ensuring the quality and efficiency of countless applications. There is a significant demand for pH sensors with versatile applications across various sectors, including agriculture, healthcare, food processing, textiles, leather, wet laboratories, and environmental remediation [1-3]. In this study, we embark on a journey of innovation and precision, focusing on the development of a cutting-edge pH sensor. Our research endeavors to address the critical need for enhanced pH sensing capabilities through a meticulously designed sensing platform, combining the unique attributes of nickel oxide (NiO) nanoparticles (NPs), polyaniline (PANI), and MXene, all ingeniously integrated onto a nickel foam (NF) electrode. The fabrication process involved a series of steps, including the synthesis of NiO NPs via the sol-gel method, following by mixing NiO and MXene, followed by further mixing with PANI and electrodeposited onto the nickel foam electrode. Fig 1 represents the fabrication process of NF electrodes with NiO/MXene/PANI composites.
The performance of the electrode was evaluated using cyclic voltammetry (CV) across various buffer solutions where NiO-PANI-MXene modified NF electrode, pt wire, and Ag/AgCl electrode were used as a working electrode, counter electrode, and reference electrode respectively. MXene are layered materials composed of transition metal carbides, nitrides, or carbonitrides. What makes MXene attractive for pH sensing is its surface functionalization, that often includes hydroxyl (-OH) and oxygen (-O) groups. These groups are responsive to variations in hydronium ion (H₃O⁺) concentration. In acidic solutions with high H₃O⁺ concentrations, these groups undergo protonation, modifying MXene's electrical properties, and affecting conductivity and potential. This alteration forms the basis for MXene's pH sensing ability, detectable through methods like open circuit potential (OCP), where changes in current at specific voltages correlate with pH levels, enabling precise pH measurements. To characterize the composites, various analytical techniques were employed. SEM-EDX, TEM and XRD were used for comprehensive structural analysis. In parallel, cyclic voltammetry (CV), amperometry, and OCP were employed to monitor shifts in potential corresponding to different pH levels within the buffer solution. The results revealed that the NiO/MXene/PANI sensor exhibited remarkable sensitivity over the pH range from 3 to 11. The pH sensor exhibits a sensitivity of 46.00 mV/pH (R2 = 0.99) and maintains consistent performance within the physiological pH range spanning from 3 to 11. This prototype currently undergoing testing alongside a commercially available pH meter using real samples, such as orange and a baking powder etc. solution. The durability and repeatability assessments have yielded encouraging outcomes. Thus, the presented NiO/MXene/PANI based pH sensor represents a significant advancement in pHsensing technology, offering improved sensitivity and stability. The incorporation of MXene within the sensing platform holds a promise for the future developments of solid-state pH sensors.
Reference

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Fig. 1. Fabrication process of NiO/MXene/PANI modified nickel foam electrode.

Figure 1