Mass Balance in a Direct Methanol Fuel Cell

Abstract

We developed a model demonstrating that the increase of fuel utilization and fuel concentration is the key to achieve the high energy density direct methanol fuel cell system. We also explain that fuel utilization and fuel concentration are closely related to crossover of methanol and water. A method that measures the methanol crossover, water crossover, and methanol utilization is presented. Unlike conventional methods, this method is not affected from the ambiguous CO 2 crossover effect through electrolyte membrane since the method is based on the methanol/water measurement at the inlet and outlet of anode and cathode. Methanol and water crossover, methanol utilization, and methanol to electricity conversion rate were measured as a function of current density, fuel concentration and anode/cathode flow rate in a single cell.

Mass transport phenomena in direct methanol fuel cells

“…The supplied liquid water on the anode can permeate the membrane and arrives to the cathode. The so-called water crossover exaggerates flooding at the cathode, which can result in a catastrophic decrease in cell performance and can inhibit robust fuel cell operation [15,23,24,26,27,30,32,40,50,51,69,[88][89][90][91][92][93][94][95]. In particular, it has recently been shown that [96][97][98] the rate of water production in the ORR at the cathode could be substantially lower than the rate of water crossover, meaning that the water flooding problem is predominately caused by water crossover through the membrane.…”

“…As a result, a water make-up system is required, making the overall DMFC system more complex and bulky. Therefore, to suppress water crossover, it is essential to gain a better understanding of the water crossover mechanisms in DMFCs, which are different from those in hydrogen-feed PEMFCs [23,26,40,59,69,78,88,91,92,[96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113].…”

“…The main operating conditions that affect water crossover include current density, operating temperature, gas flow rate in the cathode, and methanol concentration [23,69,91,[97][98][99]102,111,116]. Fig.…”

“…As a result, the water crossover due to diffusion is enhanced and the water crossover due to back convection is decreased, resulting in an increase in the watercrossover flux through the membrane. The influence of methanol concentration on water crossover has also been studied [23,91,97,102]. It was found that more water appeared in the cathode with the increase in methanol concentration, mainly due to the increased water production from the reaction of the increased methanol crossover [23,97,102].…”

Biocomposite proton‐exchange membrane electrolytes for direct methanol fuel cells

“…It is well known that the swelling properties have a huge influence on both stability and proton conductivity of a PEM . Optimal water uptake is desirable for a membrane because higher water sorption facilitates proton conduction while adversely affects the dimensional stability.…”