The effect of doping Cr on the electrocatalytic activity of supported Co2P for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution was investigated. A beneficial improvement in the performance of Co2P supported on carbon black (CrxCo2-xP/CB) towards HER and OER was discovered. For the HER at -200 mV overpotential the turnover frequency (TOF) increases almost six-fold from 0.26 to 1.52 electrons siteCo-1 s-1 when Co2P/CB has a small amount of Cr added to form Cr0.2Co1.8P/CB. Similarly, we estimate an increase from 0.205 to 0.585 electrons siteCo-1 s-1 for the OER at 1.6V for the same change in composition. With 10at% Cr doping, the Cr0.2Co1.8P/CB catalyst needed 226 mV overpotential to produce a cathodic current density of -100 A g_Co^(-1) and 380 mV overpotential to produce an anodic current density of 100 A g_Co^(-1). Based on both experimental results and theoretical calculations, the activity improvement results from optimization of electronic properties of Co2P after Cr doping.