This enzyme recycles the H(2) produced by nitrogenase to increase the production of ATP and to protect nitrogenase against inhibition or damage by O(2) under carbon- or phosphate-limited conditions. A + H2 = AH2 Binds 1 nickel ion per subunit. Heterodimer of a large and a small subunit. Belongs to the [NiFe]/[NiFeSe] hydrogenase large subunit family.