Alkaline water splitting has long been seen as a potential source of renewable hydrogen. However, the sluggish kinetics of the oxygen evolution reaction (OER) limits efficiency of such systems. Herein we report on a simple, general method for the deposition of transition metal oxides into mesoporous carbon carbon substrates and their conversion to highly active transition metal phosphides (TMP). We investigated the activity of these catalyst constructs in the presence and absence of iron impurities. The highest activity catalyst requiring an overpotential of 310 mV and a Tafel slope of 42mV/dec was our iron phosphide catalyst. We also show that the activity of the TMP construct is directly related to the presence of iron either in the catalyst itself, or as an impurity in the electrolyte.