iR Compensation for Electrocatalysis Studies: Considerations and Recommendations

Abstract

InformationC areless adoption of electrochemical methods/concepts without evaluating their applicability can lead to misleading and contradictory results.This problem is particularly apparent in recent electrocatalytic benchmarking studies such as water electrolysis and carbon dioxide reduction.As electrochemists and journal editors have repeatedly criticized, performance indicators can be exaggerated or manipulated due to overlooked preconditions, inappropriate data treatments, and misunderstood concepts.1,2 In this Viewpoint (Scheme 1), we highlight the use of iR compensation, a technique widely used in electrochemical data treatment but rarely discussed for its applicability.Brief considerations of its technical background and practical limitations in electrocatalysis research are presented, followed by operational recommendations.Technical Background.iR compensation is developed to correct for the voltage loss (i.e., iR drop) caused by the electrolyte solution between the working electrode and the reference electrode, where R stands for the resistance of the electrolyte solution.3,4 Assuming a simplified three-electrode configuration (Figure 1) with a voltage (Δϕ 1,3 ) applied between the working electrode (point 1 with the potential of ϕ 1 ) and the reference electrode (point 3 with the potential of ϕ 3 ), the potential drop between 1 and 3 can be resolved into Δϕ 1,2 (between 1 and 2) and Δϕ 2,3 (between 2 and 3).Δϕ 1,2 represents the potential drop across the electrical double layer (EDL, Δϕ EDL ), and Δϕ 2,3 is the potential drop across the bulk electrolyte (Δϕ solution ).Operationally, the working electrode's potential is controlled by adjusting the charge on the EDL.According to Ohm's law, Δϕ solution = iR solution (i, current flowing through the electrolyte; R solution , ohmic electrolyte solution resistance between 2 and 3, related to the volume of solution containing current paths between the working electrode and reference electrode).The EDL potential (Δϕ EDL = Δϕ 1,3 -iR solution ) can be calculated, namely, iR compensation.4 Traditionally, the R needed to be compensated is called R u (uncompensated resistance).In this simplified case, R u = R solution . Current Practice.In the literature, iR compensation is conducted by two methods.The most popular one is after-thescan compensation: the experimental data points are manually