Aqueous-Alkaline/Carbonate Biocarbon Fuel Cell Development

University Of Hawaii, Honolulu

Investigators

Abstract

CBET-0828006 Antal The aim of this project is the development of an aqueous-alkaline/carbonate biocarbon fuel cell which performs well while realizing electrolyte invariance by exploiting electrochemical reactions that are favored at temperatures near 300 °C. Broader impacts. Very large quantities of lignocellulosic residues (e.g. corncobs, coconut shells) accompany the production of bioethanol and biodiesel fuels. These residues can be efficiently and quickly converted into biocarbons. Carbon fuel cells can generate electricity from these biocarbons -as well as from coal, and other fossil carbons-with a theoretical thermodynamic efficiency of 100%. A recent EPRI study indicates that carbon fuel cells have the potential to convert biocarbons into electrical power at a system level efficiency of about 60%, which is over 20% higher than the efficiencies realized by current state-of-the-art integrated gasification combined cycle (IGCC) or advanced pulverized coal power generation systems. Thus the production of biocarbon can complement the production of bioethanol and biodiesel in a biomass refinery that also produces electricity at a very high efficiency. Other impacts include the training of two BS and two MS students, the involvement of Hawaii Pacific University (HPU) faculty, and the development and inclusion of new electrochemical engineering course material in the UH and HPU curricula. In view of the fact that a college degree in chemical engineering is not offered in the State of Hawaii, these impacts have special significance. Intellectual merit. This project is based on two hypotheses. 1) At temperatures approaching 300 °C the aqueous-alkaline/carbonate biocarbon fuel cell will offer an open circuit voltage (OCV) of about 1 V and a steady, maximum power density that exceeds 100 mW/cm2. 2) During operation the composition of the electrolyte will evolve towards an equilibrium mixture of hydroxide and carbonate ions that afterwards will be invariant (i.e. stable). The cathode of this cell resembles that of a Bacon fuel cell, where oxygen in air is reduced to hydroxide ion over a silver catalyst. Thermodynamic analyses indicate that the cathode should perform well at temperatures approaching 300 °C. Likewise, thermodynamic analyses indicate that at these temperatures both the hydroxide ion and the carbonate ion (formed by the reaction of CO2 with hydroxide ion) should vigorously oxidize the carbon anode and release electrons; thereby generating power at high efficiency. This project has three objectives: 1) to characterize the oxidation behavior of anodic char-coal in the aqueous-alkaline/carbonate environment of the fuel cell at temperatures near 300 °C; 2) to characterize the stability of the electrolyte, together with the catalytic effects of differing electrolytes on the anodic and cathodic reactions at temperatures near 300 °C; and 3) to characterize the performance of the biocarbon anode as a working electrode in a setup that includes a counter electrode, and flow of the electrolyte through a heat exchanger bridge to a reference electrode maintained at system pressure but at a much lower temperature.