CoNi₂Se₄ with a vacancy-ordered spinel structure shows excellent bifunctional electrocatalytic activity for water splitting in alkaline medium producing 10 mA cm⁻² at a cell voltage of 1.61 V. For OER, an overpotential of 160 mV was needed for 10 mA cm⁻² which is one of the lowest overpotentials reported to date.