Design and Development of Unconventional pH Differential Fuel Cells

Abstract

Electrochemical energy storage and conversion devices such as H2−O2 fuel cells, supercapacitors, and batteries are propelled by their potentiality to construct zero emission energy technologies. Although H2−O2 or proton exchange membrane fuel cell (PEMFC) technology is a promising zero emission technology with high efficiency, the safety and complexities associated with H2 storage projected small molecule powered direct alcohol fuel cells (DAFCs) as encouraging alternatives to H2−O2 fuel cells. However, the multielectron alcohol oxidation kinetics proceed dominantly through a parallel pathway mechanism on the benchmark Pt-based electrocatalysts, strongly blocking its catalytic domains. Secondly, alcohol crossover usually encountered in liquid fed fuel cells, eventually trigger competition at the cathodic interface and poison the Pt-based cathode catalysts. This necessitates heavy loading of precious metal cathode catalysts and engineering its catalytic domains for selective oxygen reduction reaction (ORR). All these practically hinder the commercial outreach of DAFC technology. Even though enormous efforts are dedicated to engineer the catalytic domains to favour selective ORR with inherent alcohol inertness, these strategies have so far not addressed the root of the problem, i.e., the inner sphere electron transfer nature of their half-cell chemistries. The primary aim of this thesis is the development of unconventional fuel cells by modifying the cathodic half-cell interface with pH dependent/independent redox couples. We have investigated in detail how the interfacial modification of the cathode with a pH independent outer-sphere redox couple could address some of the challenging issues with the state-of-the-art alcohol fuel cells. The modification of the cathodic interface with a pH dependent redox couple introduced additional functionality to a fuel cell wherein electricity generation is accompanied by hydrogen fuel production at room temperature and pressure which eventually lead to the development of an alcohol reforming fuel cell (ARFC). Thermodynamics of ARFC suggests that energy of neutralization is behind its operation and attempts to harvest the free energy of neutralization directly as electrical energy without a net redox lead to the development of a Fuel exhaling Fuel cell. Direct harvesting of neutralization energy without a net redox is utilized further to develop a water desalinator during electricity generation without contaminating the desalination pathway with efficiency close to the state-of-the-art RO processes.