The use of hexagonal boron nitride (hBN) to modify a semiconductor photocatalyst is one of the promising methods for the production of hydrogen from water splitting. This is due to the unique characteristics of the hBN-suppressing recombination of the photogenerated charge carriers and hence increase in the redox reactions. In the present work, a hBN-modified Ni2P-containing excess boron composite (B-hBN-Ni2P) was prepared through an electroless plating method. The solid structure, elemental composition, and morphology were investigated via X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, UV–visible spectroscopy, and photoluminescence spectroscopy. The composite coating was tested for solar water splitting, and a hydrogen evolution rate of 883 μmol/h was achieved. The role of excess B was revealed through an electrochemical acidic leaching. By gradually removing boron from the structure, a monotonous drop in the water splitting activity was observed. Our study identifies B as a sacrificial agent/hydrogen production booster. It contributes to the higher catalytic activity with an additional hydrogen generation through the oxidation of its surplus amount from the composite coating. The enhanced hydrogen evolution activity for the composite coating in the present study is highly competitive with the other modern photocatalysts.