Optimal Anode-Cathode Pairs for Galvanic Energy Harvesting in Gastrointestinal Devices

Galvanic cell development through energy harvesting in the gastrointestinal (GI) tract can provide supplementary power and prolong the deployment of ingestible devices. In this paper, we discuss the optimal choice of electrodes that can be used (in conjunction with gastric fluid - as electrolyte) in the galvanic cell. These cells comprise of a cathode and an anode, and simultaneous reduction-oxidation reactions result in the desired supplemental power. To determine the optimal cathode-anode pair, this study evaluates the performance of different cathode-anode combinations in simulated gastric conditions (pH 1.2). Cathode materials such as Pd, Pt, Cu, Ti, and Nb are examined, along with anodes Zn, Mg, and a Zn-Mg ‘hybrid’. Fifteen in vitro experiments using five different cathode choices and three different anode choices in synthetic gastric fluid (SGF, pH 1.2) were performed and analyzed in terms of parameters such as longevity and power capabilities. It was observed that Pt and Pd are the optimal choices in cathodes due to their low hydrogen reduction potential. Mg is the most suitable choice of anode in short-term gastric devices, while the anode choice in long-term gastric residency devices depends on the application, with Zn or Zn-Mg hybrid being the optimal choices. This work shows the potential for utilizing galvanic cells for supplementing on-board batteries for ingestible devices.