The practicality of an electrochemical reaction is often limited by how quickly the product can be produced. This talk will discuss ways to improve electrode structure to enable smaller reactors that produce more product. Running a reaction in a flow-through geometry, in which the reactants pass through the electrode, can increase reaction rates by increasing mass transport to the electrode surface. Carbon paper, which consists of carbon fibers 10 microns in diameter, is a common electrode used in this geometry. Part one of this presentation will describe studies of electrodes made from copper nanowires with diameters 45 times smaller than the fibers in carbon paper. The copper nanowire-based flow-through electrode increased the rate of copper ion reduction by 278 times relative to carbon paper due to its higher surface area and, to a lesser extent, its higher mass transport coefficient. An intramolecular cyclization reaction with Cu nanowire felt achieved a productivity 4.2 times higher than that of carbon paper. This rate was limited by reaction kinetics. Current efforts in this area are exploring the application of flow-through electrodes to increasing the productivity of reactions relevant to the pharmaceutical industry. The second part of this talk will discuss a comparative study of three nickel electrodes - foam, microfiber felt, and nanowire felt - for water electrolysis. The goal was to examine the tradeoff between surface area and pore structure on the efficiency and productivity of an alkaline electrolyzer. Although the nanowire felt had the highest surface area, the small pore size of the nanowire felt caused it to be quickly clogged by bubbles, even in a flow-through geometry. The open structure of the foam facilitated bubble removal, but its low surface area caused it to have the worst efficiency. The nickel microfiber felt exhibited the highest efficiency due to its high surface area as well as pores that are large enough to enable bubbled removal. The microfiber felt could maintain a current density of 25 A cm-2 for at least 100 hours. This current density is 50 times greater than conventional electrolyzers and 6.4 times greater than the next highest current density reported in the literature. Such higher production rates could lower the capital costs of alkaline electrolyzers and help to make them more economically competitive.

Increasing the rate of electrochemical conversions with microfibrous and nanofibrous flow-through electrodes

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.