Understandings on the Inhibition of Oxygen Reduction Reaction by Bromide Adsorption on Pt(111) Electrodes at Different pH Values

Abstract

Oxygen reduction reaction (ORR) is studied on Pt(111) in the presence of different concentrations of bromide anions at different pH values ranging from very acidic to neutral solutions. While adsorbed bromide inhibits the ORR, the strength of the inhibition decreases when the pH is increased. This is a consequence of the lower relative adsorption energy of bromide at higher pH values, caused by the lower absolute applied potential. This is reflected in a shift of the onset of the ORR (as measured with the hanging meniscus rotating disc electrode, HMRDE) to higher values as the pH is increased. HMRDE measurements reveal that the limiting current density (j lim) coincides with the theoretical value for two electrons only at very acidic solutions. However, when pH is increased, j lim tends toward the value for a four electrons reaction. From pH > 3 j lim coincides both in the presence and in the absence of bromide despite the specific anion adsorption. Experiments in solutions with different ionic strength and hydrogen peroxide reduction measurements suggest that the formation of a reaction intermediate different from H 2 O 2 is favored at neutral pH values.

Electrocatalysis of Oxygen Reduction Reaction on Shape-Controlled Pt and Pd Nanoparticles—Importance of Surface Cleanliness and Reconstruction

“…(Hsueh et al, 1983), halides (Cl − and Br − ) (and Marković et al, 1999; Schmidt et al, 2001; Stamenkovic et al, 2001) and other impurities (P43-, NH4+, CO, SO 2 , H 2 S, etc.) (Macia et al, 2004; Stamenkovic et al, 2005; Halseid et al, 2008; He et al, 2010; Ong et al, 2013; Rahul et al, 2015; Briega-Martos et al, 2018). Therefore, strongly adsorbing anions/cations/impurities/ in situ generated adsorbed species on the catalyst surface interfere with the investigation of dissolution and reconstruction of nanoparticles, making it is hard to investigate the stability, origin of the loss of ESA, and catalytic activity of nanoparticles.…”

Recent progress on oxygen and hydrogen peroxide reduction reactions on Pt single crystal electrodes

“…Furthermore, the onset potential in the presence of Brshifts to more positive potential values as pH increases. Additionally, measurements for the HPRR in the same conditions were carried out ( Figure 2B) [18]. In all cases the jlim measured for the ORR is higher than the sum of the theoretical jlim for a 2-electron process and the measured current for the HPRR.…”

“…3. Analogous experiments for HPRR with a H2O2 concentration that would lead to the same limiting current densities were performed, but in this case no decrease of jlim was observed ( Figure 2A) [ The mechanism of the ORR was also studied by investigating the effect of the presence of Brin working solutions with different pH values [18]. It was observed that at very acidic pH values (below pH = 1) the presence of Brreduces the jlim to the half of its theoretical value.…”

“…2B for pH = 1.1 is due to the presence of Br -, while the difference in the case of pH = 5.4 is due to the solution pH and jlim is the same in the presence and in the absence of Br -(see ref. [18]). All these results indicate that the mechanism for the ORR does not follow a sequential scheme in which H2O2 is generated as an intermediate.…”

“…There must be a bifurcation point that follows a pathway for producing water without the formation of H2O2. This intermediate was alsoproposed to be OOH • species[18].…”