The reaction of 2,6-diamino-3-[(2-carbdxymethyl) phenylazo]-pyridine (L) and CoCl2 center dot 6H(2)O affords a dinuclear cobalt (H) complex [Co2L2Cl3]Cl 1, a molecular catalyst. Electrochemical studies indicate that I can electrocatalyze hydrogen evolution both from acetic acid and purely water media (pH 7.0), with a turnover frequency of 40.64 and 750.2 mol of hydrogen per mole of catalyst per hour, respectively. Sustained proton reduction catalysis occurs at glassy carbon (GC) to give H-2 over a 48 h electrolysis period with 97% Faradaic yield and no observable decomposition of the catalyst. Photocatalytic experiments indicate that complex 1 in pH 4.0 aqueous solution under air, together with [Ru(bpy)(3)]Cl-2 and ascorbic acid as a sacrificial electron donor, in the presence of blue light (lambda(max) = 469 nm) also can produce hydrogen with a TON = 425 mol of H-2 (mol of cat)(-1). (C) 2015 Elsevier B.V. All rights reserved.