The development of efficient catalytic electrodes towards the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is at the heart of renewable-energy technologies. Despite the tremendous efforts towards engineering electrode schemes for increasing exposed surface areas and active sites, improving intrinsic catalytic activity still remains a great challenge. Here, we develop a surface-polyaniline (PANI) functionalized nickel selenide (NiSe-PANI) electrode with great performance enhancement for both the HER and OER. The decorated PANI layer subtly modulates the surface electronic structures of NiSe, with a surface-optimized selenium-enriched configuration for the HER and enhanced generation of NiIII/IV active species when oxidized for the OER. When used as a bifunctional electrocatalyst for overall water splitting, the NiSe-PANI electrode displays excellent performance, with a current density of ∼10 mA cm-2 at an applied voltage of 1.53 V during a long-term electrolysis test, and outperforms the Pt and IrO2 combination as the benchmark and most of the earth-abundant material-based bifunctional catalysts. Similar PANI-functionalization on other bifunctional nickel chalcogenide electrodes also exhibits obviously enhanced performance for overall water splitting, demonstrating the wider applicability of intrinsic activity enhancement via a surface electronic modulation strategy.