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[Display omitted] • V-Ni@NiMoO 4 /Ni 12 P 5 with a microsphere structure as the supporting framework exhibits excellent cycling stability. • For OER, a low overpotential of only 254 mV is required to achieve a current density of 50 mA cm, with no significant decline observed after 114 h of cycling. • The introduction of phosphorus enhances the electron transfer at the Ni active sites, better activating adsorbates, and thus improving catalytic performance. At present, there are few reports on the micron-sized catalysts for overall water splitting. In this study, phosphating method were used to construct the self-supporting catalyst (V doped Ni microspheres coated by NiMoO 4 /Ni 12 P 5) with microspherical structure, providing a short path and a stable structure to guarantee quick electron transfer and excellent catalytic performance. Hence, oxygen evolution reaction (OER) only needs 254 mV to reach a current density of 50 mA cm−2 in 1.0 mol/L KOH, after 114 h without attenuation. The catalyst can achieve a current densitiy of 10 mA cm−2 with a voltage of only 158 mV for hydrogen evolution reaction (HER). When micron scale V-Ni@NiMoO 4 /Ni 12 P 5 is used as both anode and cathode for overall water splitting, the device can operate at a current density of 10 mA cm−2 for more than 200 h of good stability. Its superior catalytic performance can be attributed to the construction of micron size and phosphating. DFT calculations indicate that the introduction of P better activates the adsorbed *OH and H 2 O*, reduces reaction the energy barrier, and improves the catalytic activity. [ABSTRACT FROM AUTHOR]