Impact of Ir modification on the durability of FeNC catalysts under start-up and shutdown cycle conditions

Abstract

Ir modification of FeNC catalysts improves the durability of the catalysts, but causes electronic changes that are disadvantageous for the activity.

Identification of the Catalytically Dominant Iron Environment in Iron- and Nitrogen-Doped Carbon Catalysts for the Oxygen Reduction Reaction

“…One possible reason for the contradictory structural assignments might be that the DFT predictions were typically compared to RT Mössbauer data. However, the isomer shift δ iso sensitive to the electron density at the iron nucleus and thus an important indicator for (electro)­catalytic activity , changes with temperature due to the second-order Doppler effect and depends on the local environment. Similarly, the quadrupole splitting Δ E Q associated with the electric field gradient (EFG) at the iron nucleuscan have a dramatic temperature dependence .…”

Relation between half‐cell and fuel cell activity and stability of FeNC catalysts for the oxygen reduction reaction

“…Notably, for the SSC condition, always a significant increase in the capacitance current density is observed. For the 1100°C samples, the formation of a broad redox feature associated with quinone/hydroquinone surface functional groups becomes visible as a result of partial oxidation of the carbon 40,50 . On a first view, it might appear unexpected that for the 700°C samples, the capacitance is not changing as much under the same conditions (SSC).…”

“…The start‐up and shut‐down cycle (SSC) conditions account for the high potentials that might be attained by the reverse current mode after silent periods of FCEVs 38 . Depending on the leading degradation mechanism different strategies were developed to inhibit activity losses, as the addition of small amounts of precious metals or the modification with fluorine 39–41 …”

“…A stronger pronounced COR or higher leaching rate of iron are suggested as possible origin of the larger degradation in FCs (both might also be interconnected, see statement above). In our recent work, we got indications that the COR kinetics changed more favorable from RDE to FC conditions as compared to the kinetics of the desired catalytic reactions 40 …”

“…38 Depending on the leading degradation mechanism different strategies were developed to inhibit activity losses, as the addition of small amounts of precious metals or the modification with fluorine. [39][40][41] Caution needs to be taken, when conclusions on stabilization strategies are only made on the basis of rotating (ring) disc electrode (R(R)DE) experiments rather than FC testing. While RRDE provides a good and fast platform to determine in a short period of time the kinetic current density and the hydrogen peroxide yield (if applied at low loading), these measurements are neither suited to identify mass transport limitations of the catalyst nor for fully understanding how to transfer conclusions on degradation from rotating disc electrode (RDE) to FC level.…”