In this study, we propose a highly accurate catalyst evaluation method by improving the time-zero analysis, which has been reported as an activity evaluation method for gas evolution powder catalysts. We refined the extrapolation approach to plot in this study's time-zero analysis as an analytical method. The Tafel slopes obtained with this method for LaNiO 3 (LNO) were found to be within the reported range, and the data was consistent in catalytic loading range of 2.5-3.3 mg -LNO cm −2 . Using the improved time-zero analysis, the kinetic activity of the gas evolution powder catalyst is possible to be evaluated with high accuracy.