Fe─N─C Electrocatalyst for Enhancing Fe(II)/Fe(III) Redox Kinetics in Thermo‐Electrochemical Cells

Abstract Harvesting low‐grade waste heat, which constitutes 60% of the overall waste heat, is key to halting climate change. Electrochemical waste‐heat harvesting has recently drawn attention to practical low‐grade waste‐heat harvesting. In this study, a power density maximization strategy is presented in scalable and cost‐effective aqueous redox couple‐based thermo‐electrochemical cells (TECs). The n‐type feature of the water‐soluble Fe 2+/3+ redox couple is essential for constructing the TEC p–n leg device; however, it has not been investigated much so far. The modulation of the chaotropicity of counteranions enhances the absolute value of the Seebeck coefficient for the Fe 2+/3+ redox couple with an inner‐sphere reaction mechanism because of the greater structural disorder in the solvation shell. Moreover, the use of a cost‐effective Fe─N─C electrocatalyst shows redox kinetics and a power density comparable to those of state‐of‐the‐art Pt electrodes, economically compensating for the sluggish charge‐transfer kinetics of the inner‐sphere redox mechanism. The Fe─N─C ‐based TEC device exhibits 1.73 W m −2 of power density at 0.1 $ W −1 of cost per power, which is 1.24% with respect to the Carnot efficiency, exceeding 0.23–0.53% compared to those reported for previous Pt‐based TEC devices with the same redox chemistry.