Electrocatalytic conversion of biorenewable feedstocks for electricity and chemicals cogeneration in anion exchange membrane fuel cells

Abstract

<p>Continuing depletion of world’s fossil fuel resources has been a driving factor for seeking an ultimate goal of reducing heavy US dependence on fossil fuels by extensively investigating and developing alternative fuel sources and technologies including biorefinery use of lignocellulose biomass. Electrochemistry and electrocatalysis based technologies have great potential to be used in the next generation of biorefineries, part of developing sustainable technologies to mitigate global warming and lower dependence on fossil fuels. Electrical energy could be directly generated using electrochemical fuel cell reactors based on electrocatalytic conversion processes. This might be a promising green route to partially alleviating our energy dependence on traditional fossil fuel resources. Although great progress has been achieved in selective catalytic conversion of biorenewable compounds in heterogeneous catalysis, there is still a need to explore and develop electrocatalytic biorefineries to selectively produce valuable chemicals while simultaneously generating electricity. The research efforts described in this Ph.D. dissertation are divided into two parts: applied fundamental electrocatalysis research and practical direct biorenewable fuel cell technologies development.</p> <p>First, electrocatalytic oxidation of biorenewable polyols (C3 glycerol and C4 meso-erythritol) for valuable chemicals and electricity cogeneration has been investigated on supported Pd-based nanoparticle electrocatalysts in alkaline anion-exchange membrane fuel cells. PdAg bimetallic nanoparticle catalyst has been shown more efficient than Pd for alcohol oxidation due to Pd facilitating deprotonation of alcohol in a base electrolyte, while Ag promotes intermediate aldehyde oxidation and cleavage of C-C bond of C3 species to C2 species. A mechanistic understanding of electrocatalytic oxidation of glycerol and meso-erythritol and associated bond breaking on PdAg bimetallic catalysts has been developed, and the keys influencing product distribution and reaction pathways were further elucidated and controlled by optimizing electrocatalysts and reaction conditions.</p> <p>The second part of this dissertation describes the development of practical biorenewable fuel cells technologies focused on alternative “fuel” and inexpensive durable “cells” (device). A new route for directly using complex biomass derived bio-oil as an alternative fuel to generate electricity in alkaline membrane fuel cells has been explored. Electrochemical performance of bio-oil derived from the pyrolysis of lignocellulosic biomass over precious metal monometallic catalysts such as Pt/CNT, Pd/CNT, Au/CNT, and Ag/CNT has been studied. In order to reduce costs and improve durability of fuel cell devices, the usage of porous polytetrafluoroethylene (PTFE) thin films as separators in high alkaline direct glycerol fuel cells has been thoroughly investigated. Low-cost, stable and durable PTFE thin film separators have demonstrated superior performances compared to state-of-the-art anion exchange membranes with respect to anode degradation in alkaline fuel cells under harsh alkaline conditions. Our preliminary work on integration of carbon-based cathode catalyst, porous PTFE thin film separator, and crude biorenewable fuel into a fuel cell device to generate low cost bio-electricity has shown promise toward the development of novel alkaline fuel cells with high performance, low cost, and desired durability.</p>