To avoid a massive energy crisis in the near future, it becomes urgent to develop efficient catalysts for the oxygen evolution reaction (OER) in water splitting. For this purpose, a two dimensional (2D) heterostructure of Co₃O₄ and Co₃S₄ is prepared following a simple multi-step method that incorporates a wet-chemical technique followed by a hydrothermal method. Initially, 2D sheets of Co₃O₄ are synthesized using the wet-chemical method followed by calcination. Finally, the heterostructure Co₃O₄@Co₃S₄ is fabricated from the Co₃O₄ sheets following a simple Kirkendall process through sulfurization for electrochemical application. Slow anion exchange leads to development of a hollow core@shell 2D Co₃O₄@Co₃S₄ heterostructure. After sulfidation, the heterostructure of 2D sheets shows excellent conductivity and improved electrocatalytic activity for the OER compared to bare Co₃O₄. The best-obtained Co₃O₄@Co₃S₄ can produce a 20 mA cm⁻² current density upon application of 1.647 V vs. RHE, which is ∼100 mV lower compared to bare Co₃O₄. Sulfidation of Co₃O₄ leads to the formation of hollow heterostructures with a ∼2.8 times higher electrochemically active surface area. Co₃O₄@Co₃S₄ is very stable, and it can produce an unaltered current density up to 1000 continuous cycles in the OER.