Oxygen-Evolution Reaction by a Palladium Foil in the Presence of Iron

Abstract

Herein, we investigate the oxygen-evolution reaction (OER) and electrochemistry of a Pd foil in the presence of iron under alkaline conditions (pH ≈ 13). As a source of iron, K2FeO4 is employed, which is soluble under alkaline conditions in contrast to many other Fe salts. Immediately after reacting with the Pd foil, [FeO4]2– causes a significant increase in OER and changes in the electrochemistry of Pd. In the absence of this Fe source and under OER, Pd­(IV) is stable, and hole accumulation occurs, while in the presence of Fe this accumulation of stored charges can be used for OER. A Density Functional Theory (DFT) based thermodynamic model suggests an oxygen bridge vacancy as an active site on the surface of PdO2 and an OER overpotential of 0.42 V. A substitution of Pd with Fe at this active site reduces the calculated OER overpotential to 0.35 V. The 70 mV decrease in overpotential is in good agreement with the experimentally measured decrease of 60 mV in the onset potential. In the presence of small amounts of Fe salt, our results point toward the Fe doping of PdO2 rather than extra framework FeO x (Fe­(OH)3, FeO­(OH), and KFeO2) species on top of PdO2 as the active OER sites.

Bimetallic Intersection in PdFe@FeOx‐C Nanomaterial for Enhanced Water Splitting Electrocatalysis

“…[74,75] This observation might also hint at the idea of the formation of intermetallic species, enhancing OER activity. [23][24][25][26] With respect to that possibility, the high BE observed for Pd3d 5/2 in these materials (≈336.0, and ≈338.0 eV) has been previously associated with Pd-O-Fe bonds. [76] However, these high BEs are also observed before reaction and, as previously stated, they can also be caused by the distortion exerted by the fluorinated chains of Nafion on Pd and PdO x electronic structure.…”

“…In addition, this could also indicate that oxygenoxygen bond formation takes place preferably through bimetallic rather than monometallic centers. [23][24][25][26]79,80] Therefore, the presence of a bimetallic intersection should improve reductive hydrogen adsorption of water, that occurs more efficiently than on other monometallic electrodes already reported. [67,81,82]…”

“…[6][7][8] Besides, combining a first-row transition metal such as Ni or Co with noble metals has been successfully employed to achieve multifunctional catalysts for HER/OER. [18][19][20][21][22] Recently, several works have indicated that heterometallic M-M′O x H y {hydr(oxy)oxide}intermediates (FeNi, FeCo, among others) [23][24][25][26][27][28][29] improve the OER catalytic activity versus homometallic systems, based on charge delocalization between metal centers. [24] In this direction, balancing Fe dissolution and redeposition rates over a MO x H y host establishes dynamically stable Fe active sites.…”

Workflow Engineering in Materials Design within the BATTERY 2030+ Project

“…FireWorks workflows [ 18 ] have been employed to model electrocatalysts for the oxygen reduction reaction (ORR) in alkaline fuel cells [ 54–56 ] and the oxygen evolution reaction (OER) in alkaline electrolyzers for water splitting. [ 56,57 ] As a descriptor of the thermodynamic efficiency of the electrocatalyst, the critical potential has been computed and directly compared to experimentally measured ORR and OER onset potentials. The ORR (OER) critical potential U max ( U min ) is the thermodynamic upper (lower) bound of the electrode potential for which all ORR (OER) reactions are spontaneous.…”

“…FireWorks workflows [18] have been employed to model electrocatalysts for the oxygen reduction reaction (ORR) in alkaline fuel cells [54][55][56] and the oxygen evolution reaction (OER) in alkaline electrolyzers for water splitting. [56,57] As a descriptor of the thermodynamic efficiency of the electrocatalyst, the Table 1. Interface: Jupyter (Jupyter notebook), API (application programming interface), and GUI (Graphical user interface).…”