Erroneous Evaluation on Intrinsic Activity of Electrocatalysts

Abstract

In general, the assessment of the electrocatalysts in (photo-)electrochemical system is conducted in conventional three-electrode system comprising of working, counter and reference electrodes in a batch cell configuration. Depending on the targeted electrode, the proper use of counter electrode, balancing the reaction of the working electrode, is recommended to elude possible contamination arising from the electrochemical system unexpectedly. Herein, electrochemical analyses are introduced with two different model systems, highly sensitive to the chemical changes on the surface of electrode. First, we have investigated a model reaction of hydrogen evolution reaction (HER) in a conventional three-electrode system, using p-Si as a photocathode with Pt counter electrode. Alternatively, polycrystalline platinum was used as a model cathode to investigate HER and oxygen reduction reaction (ORR) with the employment of graphite counter electrode. Substantial changes in the electrocatalytic activities were verified. Potential variations on the Pt and graphite counter electrodes were simultaneously monitored during the evaluations, of which results were coupled to the online inductively coupled plasma-mass spectrometry (ICP-MS) and in situ differential electrochemical mass spectrometry (DEMS), to monitor metal dissolution and carbon corrosion concurrently during the reactions. Significant dissolution of Pt and their subsequent redeposition on p-Si photocathode were confirmed in the former system, while strong poisoning of active Pt surface by evolved CO from graphite counter electrode was demonstrated in the latter one. Microscopic/spectroscopic analyses on the post-reaction electrodes further confirm the redeposition of dissolved species on the electrode surface. From these studies, we can suggest the most suitable form of electrochemical system based on the targeted electrode for precise evaluation.