The effects of hydride chemistry, particle size, and void fraction on micro fuel cell performance

Abstract

This paper explores the effects of fuel chemistry and pellet configuration (void fraction, particle size) on MFC reaction rate and yield. Candidate hydrides were evaluated based on their suitability in a MFC using water vapor-driven hydrolysis, and lithium aluminum hydride (LiAlH4) was selected for evaluation. Hydrogen evolution tests were performed in a hydrolysis reactor with three particle size distributions (5 μm, 20 μm, and 50 μm in mean diameter) and at three initial void fractions (86%, 71%, 43%). Void fraction and particle size are found to affect reaction rates, but have no impact on reaction yields (all were ∼100%) within the range tested. Higher void fraction and smaller particle size are correlated with faster reaction rates.Electrical discharge tests are performed on a MFC at a constant potential of 1.2 V at three particle sizes (5 μm, 20 μm, 50 μm) at a 32% initial void fraction. Tests in the MFC reveal the strong impact of particle sizes on reaction rates, and show that reaction rates decrease with increasing particle size. Reaction yields are lower (90–93%) in the MFC, which is attributed to a small hydrogen leak. The energy density of the MFC is 1003 Wh L−1, the highest reported to date.