The Establishment Of High-precision Temperature Environment Electrochemical Calorimetry System

The combination of thermo-chemical and electrochemical methods, which is called as thermo-electrochemistry, is used for studying cell reaction or half-cell reaction. In the approach, a four-dimensional data, electric potential-current-heat flow(or temperature difference)-time, can be collected and recorded simultaneously for the system studied, and are treated and analyzed based on the principles of thermodynamics, kinetics and electrochemistry. By this method, the more data than those in thermochemical or electrochemical measurements can be obtained.In this paper, the basic equation for thermo-electrochemistry (TEC) is first modified, a system for thermo-electrochemical measurements where the SRC-100 Solution-Reaction Isoperibol Calorimeter as its main part was set up and tested by the electrode reaction of the Fe(CN)₆^3-/Fe(CN)₆⁴ couple. The main results are as follows:1. The modified thermo-electrochemical equation for the entropy change of a half-cell reaction has been derived asThe entropy change of half-cell reaction on absolute scale in a given concentration can be obtained from a set of the experimental data ofΔV(t)-t andη_k(t)-t curves obtained by the electrode polarization in constant current.2. The system for thermoelectrochemical measurements, which consisted of a SRC100 Solution-Reaction Isoperibol Calorimeter, a heat-sensor and a CHI660B electrochemical workstation, was assembled. The cyclic voltammetry in 0.01mol·L^-1 K₃Fe(CN)₆+0.01mol·L^-1 K₄Fe(CN)₆+1mol/L KCl solution has used for testing the reliability for the system. The calorimeter gives the studied system a nicer thermostat with±0.001 K temperature fluctuations, a data Acquisition program, which is visual and simple to operate, a main frame which contains Wheatstone bridge, microvolt amplifier, potentiostat, constant current source and USB data acquisition module. The thermistor with the good linearity between resistance and temperature and more sensitive is selected to make a heat-sensor electrode.3. The cathode reaction for Fe(CN)₆^3-/Fe(CN)₆^4- couple was studied by the differential-thermometry technique using thermistor as the element of measuring temperature. The entropy changes of this half-cell reaction on absolute scale are determined under different concentrations, which are close to those in literature.