Changes of the surface structure of corn stalk in the cooking process with active oxygen and MgO-based solid alkali as a pretreatment of its biomass conversion

► Corn stalk was cooked by a novel cooking method - active oxygen cooking with a solid alkali. ► This cooking can effectively remove lignin and extractives. ► There is a pitting corrosion on the surface of corn stalk pulp. ► The OC-O-component increased on the surface of pulp after cooking. ► The surface of corn stalk pulp became granular and relatively smoother after cooking.