Comparative investigation of NADH electrooxidation at graphite electrodes modified with two new phenothiazine derivatives

► Modified electrodes with two new phenothiazine derivatives. ► The voltammetric response was not affected by the substituent at positions 3 and 7. ► The modified electrodes showed electrocatalytic activity for NADH oxidation. ► Besides the thermodynamic driving force the surface coverage strongly influenced the electrocatalytic efficiency.