Complete Solid State Dissolved Oxygen Sensor Using Hemin Electrocatalyst and Palladium-Reusable Reference Electrode

Dissolved oxygen (DO) is essential for aquatic life, but is consumed during the decomposition process of the organic matter in water. It is used as a primary indicator of water quality, and is also crucial for the efficiency of the waste water treatment process. Hence, a sensitive, long term reliable, in-line DO sensor is essential for sustainability of water ecosystems and management of water resources. This paper introduces a low-cost, all-solid state DO sensing device by the integration of polyhemin-based DO sensitive electrode and Pd/H reference electrode. Low cost electrodeposition techniques are applied in both the DO sensitive electrode and the Pd/H reference electrode synthesis. First, the operation parameters of the Pd/H reference electrode was characterized to obtain the adequate lifetime and response time of reference for DO sensing application. The regeneration procedure of the reference electrode is also investigated to achieve multi-usage of this Pd/H electrode. Consequently, this DO sensing device has a sensitivity of 1.3 ( $\mu \text{A}$ /cm2)/(mg/L) over a DO concentration range of 1.5 – 20 mg/L. The DO sensing applications in various water samples including tap water, simulated surface water and wastewater are also demonstrated. The all solid-state feature allows this sensing device to be applied as a long-term DO sensor for continuous, in-situ water monitoring.