Balanced flow distribution to each cell in a fuel cell stack plays a significant role in the stack being able to operate at maximum capability and efficiency. This paper discusses the performance improvements in proton exchange membrane fuel cell stacks that can be obtained by using cell-to-cell flow distribution control. In a specially instrumented four-cell stack that employs needle valves to externally control the air and fuel flows to each cell, fuel to a single cell was reduced. The V-I curves collected under these conditions (unbalanced) are compared to curves collected when the fuel flow to each cell was equal (balanced). Reducing the fuel flow to a single cell by 30% decreased the V-I curve cutoff load by 8.5% — demonstrating the negative effect that unbalanced fuel flows can have on stack performance. Typical fuel cell stacks have no dynamic means to keep flows in the stack balanced between the cells, but this work indicates that flow balancing among cells can extend the V-I curve for a fuel cell to higher current values, allowing fuel cell stacks to operate reliably at higher loading and fuel utilizations. Plans to use novel, custom-built micro-valves to dynamically balance flow to individual cells in a fuel cell stack are being pursued as a result of this work, and the status of this development effort is provided.

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