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• Amorphous Co-P-B electrocatalyst synthesized by facile non-toxic reduction method. • Co-P-B shows excellent bifunctional behaviour in alkaline medium. • Co-P-B inherits electron transfer properties from both Co-B and Co-P. • DFT studies identified Co sites in Co-P-B more favourable for H-adsorption. • Wide-pH suitability and stability was established for Co-P-B catalyst. A unique cobalt-phosphide-boride (Co-P-B) catalyst was synthesized via simple chemical-reduction route. The obtained catalyst was amorphous in nature, resembling the spherical morphology of Co-B nanoparticles. X-ray photoelectron spectroscopy revealed that B loses electrons to Co while P gains electrons from Co. This unique electron transfer mechanism in Co-P-B is a combination of the characteristics showcased by Co-B and Co-P catalysts individually. The optimized catalyst (Co-P-B-5) showed overpotentials of 145 mV and 290 mV to achieve the benchmark current density of 10 mA/cm2 for HER and OER, respectively, in 1 M NaOH. From theoretical calculations, it was observed that addition of P modulates the electron density at Co sites, thereby optimizing the H-adsorption capability, leading to higher HER rate. During anodic polarization, Co-P-B-5 shows formation of large number of CoOOH species on its surface, facilitating OER. Finally, stability, recyclability and wide-pH suitability of Co-P-B-5 was established to demonstrate its industrial viability. [ABSTRACT FROM AUTHOR]