Enhancing catalytic water-splitting activity under mild environments is significant to solve the long-standing cost, safety and stability issues in photoelectrochemical cells. Here, we demonstrate the crucial role of improving surface H transfer in achieving efficient water-splitting catalytic activity of Co3O4 nanowire arrays in near-neutral pH working electrolytes. Under weak OH circumstances, the impedance of mass transfer quickly multiplies and the catalytic current declines to a current plateau in the region of 1.7-2.1 V vs. RHE, due to the surface H concentration approaching a threshold value in the range of 10(-3)-10(-4) M. The proper choice of buffering agents to facilitate the mass transfer, with 0.1 M KPi as a prototype, would decrease the overpotential by 500 mV for neutral electrolyte and favors to achieve a catalytic current comparable to that under strong alkali environments (pH > 13). These results also provide a solid guideline for extending the electrocatalytic utility of other transition metal catalysts to near-neutral pH environments. (C) 2013 Elsevier Ltd. All rights reserved.