Advanced Evaluation of the Long-Term Stability of Oxygen Evolution Electrocatalysts

Abstract

Evaluation of the long-term stability of electrocatalysts is typically performed using galvanostatic polarization at a predefined current density. A stable or insignificant increase in the applied potential is usually interpreted as high long-term stability of the tested catalyst. However, effects such as (i) electrochemical degradation of a catalyst due to its oxidation, (ii) blocking of the catalyst surface by evolved gas bubbles, and (iii) detachment of the catalyst from the electrode surface may lead to a decrease of the catalyst's active surface area being exposed to the electrolyte. In order to separate these effects and to evaluate the true electrochemical degradation of electrocatalysts, an advanced evaluation protocol based on subsequently performed electrochemical impedance, double layer capacitance, cyclic voltammetry, and galvanostatic polarization measurements was developed and used to evaluate the degradation of IrO2 particles drop-coated on glassy carbon rotating disk electrode using Nafion as a binder. A flow-through electrochemical cell was developed enabling circulation of the electrolyte leading to an efficient removal of evolved oxygen bubbles even at high current densities of up to 250 mA/cm(2). The degradation rate of IrO2 was evaluated over 225 test cycles (0.733 ± 0.022 mV/h) with a total duration of galvanostatic polarization measurements of over 55 h.

Polybenzoxazine‐Derived N‐doped Carbon as Matrix for Powder‐Based Electrocatalysts

“…In situ Raman spectroscopy (Figure S16) indicates that the transition metal oxides are mainly responsible for catalyzing the OER whereas the N‐doped carbon matrix facilitates electrical interparticle connection. A recently developed stability assessment methodology was applied to evaluate the carbon–Mn x Co y O z catalyst and showed a negligible change in activity at current densities of 1.4 and 10 mA cm −2 (Figure c). Additional stability measurements were conducted using carbon–Mn x Co y O z ‐modified Ni foam in a custom‐built flow‐through cell .…”

“…A recently developed stability assessment methodology was applied to evaluate the carbon–Mn x Co y O z catalyst and showed a negligible change in activity at current densities of 1.4 and 10 mA cm −2 (Figure c). Additional stability measurements were conducted using carbon–Mn x Co y O z ‐modified Ni foam in a custom‐built flow‐through cell . During the accelerated galvanostatic stability test with an applied current density of 10 mA cm −2 (with respect to the exposed surface of ø=8 mm), the corresponding potential increased from an initial value of 1.61 to 1.68 V versus RHE after 67 h (Figure d).…”

Impact of the Co : Cu Ratio in CoCu‐Containing Oxidic Solids on their Activity for the Water‐Splitting Reaction

“…Otherwise, a number of alterations might take place during galvanostatic polarization due to solid state changes, leaching phenomena, oxygen bubbles formation etc. that can influence the long‐term behavior …”

“…5.7 μL of the catalyst suspension was dropped on the glassy carbon electrode area and dried at room temperature in ambient atmosphere. The resulting catalyst loading was 250 μg/cm 2 …”

“…Onset‐potentials were deduced from logarithmic form of LSVs. Galvanostatic stability measurements (GSS) were done at the current density of 10 A/g catalyst (=2.5 mA/cm 2 electrode area ) for 900 s …”