Tailoring valence electron delocalization of transition metal center is of importance to achieve highly-active electrocatalysts for oxygen evolution reaction(OER).Herein,we demonstrate a“poor sulfur”route to synthesize surface electron-deficient Co9S8 nanoarrays,where the binding energy(BE)of Co metal center is considerably higher than all reported Co9S8-based electrocatalysts.The resulting Co9S8 electro-catalysts only require the overpotentials(η)of 265 and 326 mV at 10 and 100 mA cm-2 with a low Tafel slope of 56 mV dec-1 and a 60 h-lasting stability in alkaline media.The OER kinetics are greatly expedited with a low reaction activation energy of 27.9 kJ mol-1 as well as abundant OOH* key intermediates(24％),thus exhibiting excellent catalytic performances.The surface electron-deficient engineering gives an available strategy to improve the catalytic activity of other advanced non-noble electrocatalysts.