▎ 摘　　要

High quality graphene sheets have been considered as a promising candidate in several industrial applications due to their excellent electronic and thermal conductivity. However, the mass production of high quality graphene sheets from graphite bulk is still facing great challenges. Here we demonstrated a new approach to prepare high quality graphene by mixing a solution of oxalic acid and hydrogen peroxide as the electrolyte. The reaction did not involve the oxidation of graphite and thus exfoliated graphene possesses a uniform lateral size (2-6 mu m, 78.1%), low oxygen content (2.41 at. %), few structure defects, and high conductivity of 26 692 S m(-1). The optimized mixed electrolyte is environmental friendly, cheap and safe, and most importantly it is easy to be removed through low temperature heating, which facilitates graphene purification. An electrothermal heater, made from highly concentrated graphene ink (8.5 mg mL(-1)) on A4-size paper or polyester, exhibits excellent performance: a rapid rise of temperature (up to 75.2 degrees C) in a short time (30 s) under a low voltage of 10 V. The as-made graphene is considered as a promising material for future application of printable electronics and wearable devices.