Regenerative microfluidic fuel cell for high efficient H2 production and utilization

Abstract

Microfluidic fuel cell (MFC) is a novel type of fuel cell. It utilizes unique laminar-flow interface to naturally separate the fuel and oxidant streams without need of a membrane. We recently developed a new concept of regenerative microfluidic fuel cell (RMFC) to make a single cell perform dual functions: as a MFC to supply electricity and as a microfluidic electrolysis cell (MEC) to produce fuel. Here, a proof-of-concept prototype of RMFC will be presented. We leverage microfludic principles to break thermodynamic constraint on RMFC. The membraneless nature of RMFC enables individual tailoring of the composition of anolyte and catholyte without the need to consider the membrane stability subject to pH environment, thus allowing the kinetics and thermodynamics at the anode and cathode to be optimized independently and dynamically. Certain combinations of anode and cathode pH media will result in very low open circuit potentials (OCPs), while others may lead to high OCPs as a result of the pH dependence of standard electrode potentials, which will be respectively favorable for EC and FC applications. For example, both conventional alkaline and acid FC and EC achieves OCP of 1.23 V. While combining the acid O2 electrode with alkaline H2 electrode in a MEC, the OCP is lowered to 0.51 V, which thermodynamically requires 58% lower voltage to drive water splitting. Vice versa, by coupling acid H2 and alkaline O2 electrodes in a MFC, the OCP increases to 1.94 V, providing a significantly higher power output. As such, both FC and EC operation can be enhanced. Thermodynamically, the cycle efficiency for a H2 RMFC can be as high as 380%. Practically, efficiency exceeding 100% is achieved.