Better than platinum? Fuel cells energized by enzymes

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Abstract
Dihydrogen (H2) gas has the potential to be a limitless source of clean energy if simple and efficient methods of production and utilization can be developed. In that regard, using H2 to store electrical energy by means of an electrochemical cell and returning that energy by means of a fuel cell would be among the cleanest and most efficient energy methodologies. This electrochemical apparatus needs to employ robust catalysts for proton reduction and dihydrogen oxidation. In a nonbiological setting, these processes are most readily accomplished at a platinum electrode. Unfortunately, platinum is resource-limited, expensive, and irreversibly inactivated by common trace impurities in H2 gas, such as H2S and CO. In a biological setting, proton reduction and dihydrogen oxidation is most readily accomplished by the sulfur-bridged di-iron and nickel-iron active sites of the hydrogenase enzymes (Fig. 1) (1-8). Almost immediately after their discovery, the prospect of replacing expensive noble metal catalysts by these base metal-containing enzymes was recognized (9). The [FeFe] hydrogenase enzyme from Megasphaera elsdenii has been shown to catalyze proton reduction …