The Untold Tale of the ORR Polarization Curve

Abstract

A rotating disk electrode (RDE) is employed to screen materials for the electrochemical oxygen reduction reaction (ORR), which is a key reaction in fuel cells and metal−air batteries. Nevertheless, even more than seven decades after the first report on RDE and the exponential growth of publications on ORR, the following questions remain unanswered: how are the ORR polarization curves related to the fuel cell polarization and power density curves, and what is hidden in the sigmoidal nature of ORR polarization curves? Here, we have made an effort to unveil various aspect of ORR polarization curves and ORR parameters such as the onset, half-wave potential, and diffusion-limited current density from the fuel cell prospective. Interestingly, we find one-to-one mapping among the matrices used to apprise the ORR and fuel cells. It is remarkable that the slope is close to unity for the fuel cell matrices and that it is projected from the ORR polarization curves. This analysis will be a great help to researchers for appraising the suitability of their designed/developed electrocatalysts targeted for fuel cells and metal−air battery applications.

FeCoNiMnCr High-Entropy Alloy Nanoparticle-Grafted NCNTs with Promising Performance in the Ohmic Polarization Region of Fuel Cells

“…The cathode electrocatalysts with narrow potential windows have been envisioned as appropriate candidates for practical fuel-cell application as they are expected to be more tolerant to fuel-cell working voltage drop in the Ohmic polarization region during useful current withdrawal. 33 This can be further elucidated by exploring the LSV-ORR polarization curves and rearranging them to construe the projected fuel-cell polarization curves (Figure 4b). Though the activation polarization of HEA-grafted NCNTs is slightly larger than that of Pt−C (Figure 4c), which is in agreement with their comparative E onset (E onset_Pt−C ∼ 975 mV, E onset_HEA ∼ 945 mV), importantly, the polarization losses in the linear or Ohmic region (operational window from a practical-application point of view, Figure 4c) are comparatively more for Pt−C than for the HEA system.…”

Uniform Distribution of Ruthenium Nanoparticles on Nitrogen-Doped Carbon Nanostructure for Oxygen Reduction Reaction

“…44,45 Furthermore, the fuel cell performance has been predicted on the basis of the RDE polarization curve. 6 Therefore, we believe that the DOE target can also be applied to the half-cell level in alkaline medium as well. In contrast, the loss is 28% after 7000 cycles for Pt/C under the same experimental condition.…”

“…The major loss of power in the fuel cell system is due to ORR which occurs at the cathode. Therefore, almost the overall overpotential of MEA is mainly decided by ORR owing to the complexity that occurred due to the involvement of the multielectron transfer process coupled with the adsorption/desorption of reaction intermediates. , Furthermore, the fuel cell performance has been predicted on the basis of the RDE polarization curve . Therefore, we believe that the DOE target can also be applied to the half-cell level in alkaline medium as well.…”

“…The rapid increase in energy demand has sped up the hunt of green and electrochemical energy conversion and storage devices such as fuel cells and metal–air batteries. − At the cathode side of these devices, oxygen reduction reaction (ORR) takes place that requires an electrocatalyst. − In order to design an efficient ORR electrocatalyst, it is vital to comprehend the fundamental insight associated with the electron transfer from the electrocatalysts to oxygen molecule. − Both the inner-sphere electron transfer (ISET) and outer-sphere electron transfer (OSET) mechanisms, especially in alkaline media, coexist during the ORR process . ISET includes the direct interaction of electroactive centers with desolvated oxygen molecule at the inner Helmholtz plane (IHP) via direct/series 4e – transfer, whereas OSET involves the indirect interaction of electroactive centers with the solvated oxygen molecule in the vicinity of the outer Helmholtz plane (OHP), promoting a 2e – ORR pathway and generating stable HO 2 – as a reaction intermediate. ,− The energy efficient direct/series 4e – ISET mechanism during ORR is key for the realization of an efficient and stable oxygen electrocatalyst.…”

Axial ligand engineering for highly efficient oxygen reduction catalysts in transition metal–N4 doped graphene

“…[1][2][3][4][5] Electrochemical oxygen reduction reaction (ORR) is an essential process for energy conversion devices such as fuel cells and water splitting, and it determines the energy conversion efficiency. [6][7][8][9] Platinum (Pt) and Pt-based compounds are known to have excellent catalytic performance in the oxygen reduction process. [10][11][12] However, they are prone to be deposited by carbon and to be poisoned by carbon monoxide, and the commercial cost is also high.…”