A universal method for N/B codoped carbon bubbles for enhanced potassium ion storage

•N, B co-doped porous carbon was prepared by a self-templating method.•Na2B4O7 plays an important role in the formation of carbon bubbles.•N, B doped carbon bubbles exhibit high reversible capacity and long-term stability.•Pseudocapacitance dominates capacity storage in potassium ion batteries.