Design and development of direct glucose alkaline fuel cells

Abstract

The development of direct glucose fuel cells or glucose sensors in-vivo or in-vitro for the measurement of glucose concentration in the human blood is desirable for medical applications. An implantable, miniature, accurate and reliable sensor to monitor the glucose concentration in the body is desirable for treatment of diabetes mellitus. An implantable glucose-oxygen fuel cell has been proposed for artificial hearts using glucose and oxygen in the blood as the reactant. A practical fuel cell system has not yet been developed for this application, however. The electrocatalytic glucose sensor and glucose fuel cell are based on the catalytic glucose oxidation on an electrode surface which produces a current related to the concentration of glucose. Different electrodes have been investigated for glucose electrooxidation, e.g. platinum [1-6], gold [7-11], glassy carbon [12, 13], cobalt, rhodium and iridium [12-15], nickel and palladium [12, 13, 15], copper and silver [12, 13], phthalocyanines and porphyrins complexes of cobalt, manganese and iron [12]. Moreover, glucose oxidation has been studied in acid [16], neutral [16, 17] and alkaline [18] solutions. In literature there are few works [3, 19] concerning the study of glucose electrooxidation on Pd-based/C electrocatalysts, in alkaline environment. In the present Ph.D thesis, firstly literature review was conducted in order to identify the most efficient and studied electrocatalysts for direct-liquid proton exchange membrane fuel cells. In sequence, the literature review was continued including also the novel type of direct liquid anion exchange membrane fuel cells. According to the above reviews platinum was recognized as the best electrocatalyst for direct liquid-fed proton exchange membrane fuel cells, while palladium was identified as the best one for direct liquid-fed anion exchange membrane fuel cells. The first step of design and development of fuel cells is the recognition of the most active electrocatalysts towards anode and cathode reaction. To this purpose, in the present work binary Pd-based electrocatalysts were prepared and were investigated as anode electrocatalysts for glucose electrooxidation in half direct glucose alkaline fuel cells. More precisely, PdxRuy (20 wt%)/C, PdxRhy (20 wt%)/C and PdxSny (20 wt%)/C are studied as anode direct glucose alkaline fuel cells’ materials, while PdxAuy (20 wt%)/C is investigated as glucose sensors’ material. The above-mentioned electrocatalysts and the respective results are reported for first time in literature, indicating the novelty of the present PhD thesis. For the preparation of the examined electrocatalysts a modified-microwave assisted polyol method was used. The physicochemical characterization of electrocatalysts was conducted by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy-Energy Dispersive X-RaySpectroscopy and Thermogravimetric Analysis (TG). The electrochemical characterization was carried out with the Cyclic Voltammetry (CV-half direct glucose alkaline fuel cell), Rotating Disk Electrode Technique (RDE) and Chronoamperometry techniques (CA). At room temperature Pd3Sn2/C and PdRh/C presented almost the same activity towards glucose electrooxidation; however the first one presented higher poisonous rate. Considering the activity (good activity) and poisonous-tolerance together (the highest among the examined electrocatalysts), Pd30Au70/C was chosen for being studied as glucose sensor. Moreover, the effect of glucose’s, electrolyte’s concentration and temperature were studied, extracting important kinetic parameters for glucose’s electrooxidation reaction. Increasing glucose’s and electrolyte’s concentration, current density was enhanced for all the examined electrocatalysts, except for PdxRhy/C ones over which for electrolyte’s concentration higher than 1 M KOH current density was suppressed. Finally, glucose electrooxidation reaction current density was increased increasing temperature until 40oC. For higher temperature values glucose’s alkaline solution was observed to degrade forming a dark yellow caramel line smell liquid, decreasing current density values. For T>30oC, PdRh/C is suggested as anode material for glucose electrooxidation reaction, while Pd30Au70/C as glucose sensors’ material. Future outlooks are the optimization of the electrocatalysts’ preparation method as well as of the PdRh/C and Pd30Au70/C electrocatalysts and the development of a single direct glucose alkaline fuel cell.