Nature-inspired hierarchically structured high-efficiency PEM fuel cell

Abstract

Proton exchange membrane (PEM) fuel cell technology is a promising means of producing clean and efficient energy. PEM fuel cells produce electric power through the electrochemical reaction of hydrogen, derived from fossil or renewable fuels, and oxygen. However, several fundamental factors continue to hamper extensive commercialization of PEM fuel cell technology. These factors include: inefficient utilization of expensive precious metal catalysts, performance loss caused by transport limitations, catalyst stability, and water management.

We demonstrate an optimized fractal gas distributor structure for the cathode of a PEM fuel cell by constructing and characterizing a nature-inspired fuel cell based on mechanistic, hypothesis-driven optimization principles guided by fractal geometry. In addition, a robust model including detailed electrochemical kinetics is introduced which describes multiple transport and reaction phenomena that occur within the electrocatalytic layer(s). Subsequent optimizations of the cathode electrocatalytic layer with respect to two distinct objective functions, maximizing platinum utilization (PU kW/gPt) and maximizing power density (PD W/cm2) are reported. Results suggest an order-of magnitude improvement in platinum utilization is within reach.

This work aims to construct a platform on which each of these factors can be addressed based on an optimized, hierarchical design extending from the nano-scale cathode catalyst layer to the macro-scale bipolar plate flow field design. The novel, nature-inspired, fractal-based design is aided by computer simulations, which are guided by the remarkably efficient and robust, hierarchical structure of the human lung. The lung's architecture exhibits three attractive features that will be translated to materials design: (1) an ability to bridge length scales, and easily scale-up - irrespective of size - while preserving microscopic function (cells in the lung, active sites in catalysis); (2) realizing uniform distribution of various species (molecular and ionic); (3) minimizing transport resistance and thermodynamic losses, via optimized dimensioning of the hierarchical channel size distribution.