Best Practice for Evaluating Electrocatalysts for Hydrogen Economy

Abstract

Screening new electrocatalysts is key to the development of new materials for next-generation energy devices such as fuel cells and electrolysers. The counter electrodes used in such tests are often made from materials such as Pt and Au, which can dissolve during testing and deposit onto test electrocatalysts, resulting in inaccurate results. The most common strategy for preventing this effect is to separate the counter electrode from the test material using an ion-transporting Nafion membrane. Here, we use X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis, mass spectrometry, and voltammetry to demonstrate the limitations of this approach during constant-current, extended stability testing of electrocatalysts for H2 evolution. We show that Nafion membranes cannot prevent contamination of carbon electrocatalysts by Pt and Au counter electrodes, leading to an apparent increase in electrocatalytic activity of the carbon. We then demonstrate that carbon counter electrodes in undivided cells can contaminate and deactivate Pt and Au electrocatalysts for H2 evolution. We show that use of a setup comprising a glass frit separating a carbon counter electrode from the test electrocatalyst can prevent these effects. Finally, we discuss these phenomena using H2 evolution at MoS2 and at a K6[P2W18O62](H2O)14/carbon nanotube composite as test reactions.

Palladium Nanoparticles Hardwired in Carbon Nanoreactors Enable Continually Increasing Electrocatalytic Activity During the Hydrogen Evolution Reaction

“…Encouraged by the initial HER cycling tests, the electrochemical performance of PdNP@GNF was tested over a larger number of cycles, up to 30000 cycles, and compared with that of the Pt/C electrocatalyst benchmark after 5000 and 30000 cycles under the same conditions (Figure 3 c,d and Figure 4 ). It is worth noting that accelerated durability tests were carried out using a carbon counter electrode, which rule out Pt dissolution‐redeposition effects[ 54 , 55 , 56 ] on the observed electrochemical performance. It is remarkable that as the number of HER cycles increases, the performance of the PdNP@GNF catalyst continues to improve, overtaking Pt/C after about 15000 cycles (Table 1 and Figure 4 c).…”

An alternative, low-dissolution counter electrode to prevent deceptive enhancement of HER overpotential

“…Then, the dissolved Pt ions redeposit on the surface of the working electrode, resulting in deceptive enhancement in the measured overpotential 4 , 6 , 7 . Furthermore, even when an ion exchange membrane (Nafion) is used, Pt dissolution and deposition on the working electrode still takes place 8 . These concerns necessitated the search for alternative counter electrodes.…”

Reliable Counter Electrodes for the Hydrogen Evolution Reaction in Acidic Media

“…An example of Pt interference is the significant HER performance increase with carbon materials. , Our experiments (Figure S1) also confirm Pt contamination in a carbon electrode. Using two compartments to separate the WE and CE can mitigate this effect to some extent, though an article by Walsh et al reveals that even an ion-exchange membrane (e.g., Nafion) cannot completely prevent Pt deposition on the WE . This issue has led the electrocatalysis community to transition from Pt CEs to carbon-based materials (e.g., graphite or glassy carbon).…”

“…Using two compartments to separate the WE and CE can mitigate this effect to some extent, though an article by Walsh et al reveals that even an ion-exchange membrane (e.g., Nafion) cannot completely prevent Pt deposition on the WE. 7 This issue has led the electrocatalysis community to transition from Pt CEs to carbon-based materials (e.g., graphite or glassy carbon). The last two years of American Chemical Society literature, where carbon materials are described in approximately two-thirds of the articles, supports this observation.…”