'Total electrode' and 'intrinsic' activity parameters in water electrolysis: a comprehensive investigation

The fastest and greenest method of manufacturing bulk hydrogen with the highest purity is electrochemical water splitting, which is powered by electrical energy produced from renewable sources. Researchers are devoted to enhancing the electrocatalytic properties of the materials that catalyze the electrochemical water splitting via oxygen evolution reaction (OER) at the modified electrodes (anode) and the hydrogen evolution reaction (HER) at the cathode owing to the recently revolutionary discovery of nanomaterials, in response to the sudden and exponentially increasing interest in this field. This has led to many unreported and inadvertent mistakes, which are primarily the result of a lack of clear understanding of the activity parameters. Two main categories of activity parameters are usually used to certify an electrocatalyst, namely, 'total-electrode' or 'extrinsic' parameters and 'intrinsic' activity parameters. From an experimental and theoretical standpoint, we have shown how various extrinsic parameters are largely influenced by several physical parameters, such as mass loading and scan rate, thus unable to reflect the molecular origin of the improved electrocatalytic activity. On the other hand, various intrinsic activity markers, such as turnover frequency (TOF), and faradaic efficiency (FE) enable us to dig into the molecular origin of electrocatalytic activity. Herein, we systematically investigated the dependence of extrinsic activity parameters on various physical parameters with details of experimental results and analysis for the first time. Moreover, for the first time, we have highlighted that even though TOF is considered an intrinsic marker, the conventional mathematical pathway is not free from dependency on mass loading, scan rate, and substrate effects. Overall, this novel analysis would help researchers to understand the importance of reporting various activity markers and their proper reporting for the future development of various electrocatalysts intended for water splitting and other electrocatalytic applications. Various electrochemical activity markers were distinguished based on their intrinsic and extrinsic behaviours. A detailed experiment portrays the importance of properly reporting the activity in terms of intrinsic electrochemical parameters.