Effect of the structure of imidazolium cations in [BF4]−-type ionic liquids on direct electrochemistry and electrocatalysis of horseradish peroxidase in Nafion films

► [BF4]−-type ionic liquids (ILs) with different alkyl groups on imidazole ring as supporting electrolytes. ► The HRP electrode without any mediators facilitates the clarification of the single effect of ILs on the direct electrochemistry and electrocatalysis. ► Nafion film rejects [BF4]−, highlights the effect of cations and reduces the potential interference of F−.