This work reports, for the first time, Co-Mo-B as a bifunctional electrocatalyst, prepared by a facile reduction method. The optimized catalyst, Co-3Mo-B shows excellent HER performance and achieves 10 mA/cm2 at mere 96 and 66 mV (vs RHE) in pH 7 and pH 14, respectively with good stability (40 hours) and reusability (5000 cycles). Co-3Mo-B catalyst is found to be made up of nano-sized crystalline domains, separated by grain boundaries containing active under-co-ordinated sites. From morphological, physico-chemical and electrochemical analyses, it was found that Co-3Mo-B nanoparticles (NPs) exhibit small size (similar to 18 nm) with high specific and electrochemical surface area. Under alkaline conditions, Co3Mo- B can also produce oxygen at meagre overpotentials (10 mA/cm(2) at 320 mV) with favourable stability. Bifunctional property is demonstrated by employing Co-3Mo-B in a 2-electrode alkaline cell to execute overall water electrolysis, producing 10 mA/cm(2) at just 1.69 V, which is maintained for at least 25 hours of operation. The nature of the catalyst to form Co oxide/hydroxide species on the surface is responsible for good OER performance. The significant activity of Co-3Mo-B makes it the best metal boride bifunctional electrocatalyst reported so far. (C) 2017 Elsevier Ltd. All rights reserved.