Comment on “The electrochemical Peltier heat of the standard hydrogen electrode reaction” by Zheng Fang et al.

Fang et al. recently performed electrochemical Peltier measurements, proposed an absolute entropy scale for the standard hydrogen electrode, and gave a value for the partial molar entropy of hydrogen ions in solution. That paper contains several ambiguities and omissions that should be resolved in order to make the information in the paper more useful. The thermodynamic state of the electron in their treatment is not fully specified, and the method used to calculate the partial molar entropy of solution phase hydrogen ions is not given. Furthermore, the calculation of partial molar entropy of solution phase hydrogen ions apparently omits the partial molar entropy of metal-phase electrons, a term that is necessary for such determinations if the starting point is electrochemical Peltier heat measurements. As a smaller matter, the paper overlooks specifying the units used for fugacity. The paper also overlooks previous work on absolute half-cell entropy.