Construction of high-efficiency electrochromic electrodes with large and fast optical modulation is important for development of advanced smart windows. In this work, we report highly porous metal oxide (Co3O4) nanowall arrays via solvothermal method. Noticeable porous structure and cross-linked network are realized in the interconnected Co3O4 nanowalls. Improved porosity and faster ion/electrons transportation are combined in this unique nanowall architecture. The electrochromic properties of Co3O4 nanowall arrays are characterized via optical-electrochemical measurements. Cyclic voltammetry and transmittance tests demonstrate that the interconnected Co3O4 nanowall arrays show larger (52% at 632 nm) and faster (0.8-0.9 s) modulation of yellow-brown light, and higher electrochemical reactivity and smaller polarization as compared to the common Co3O4 nanowall arrays (31% at 632 nm with 1.3-1.5 s). The enhanced optical modulation is owing to the porous cross-linked nanowall structure with more active sites and shorter diffusion paths for ions/electrons. (C) 2017 Elsevier Ltd. All rights reserved.