In Situ Mechanistic Insights for the Oxygen Reduction Reaction in Chemically Modulated Ordered Intermetallic Catalyst Promoting Complete Electron Transfer

Abstract

The well-known limitation of alkaline fuel cells is the slack kinetics of the cathodic half-cell reaction, the oxygen reduction reaction (ORR). Platinum, being the most active ORR catalyst, is still facing challenges due to its corrosive nature and sluggish kinetics. Many novel approaches for substituting Pt have been reported, which suffer from stability issues even after mighty modifications. Designing an extremely stable, but unexplored ordered intermetallic structure, Pd2Ge, and tuning the electronic environment of the active sites by site-selective Pt substitution to overcome the hurdle of alkaline ORR is the main motive of this paper. The substitution of platinum atoms at a specific Pd position leads to Pt0.2Pd1.8Ge demonstrating a half-wave potential (E 1/2) of 0.95 V vs RHE, which outperforms the state-of-the-art catalyst 20% Pt/C. The mass activity (MA) of Pt0.2Pd1.8Ge is 320 mA/mgPt, which is almost 3.2 times better than that of Pt/C. E 1/2 and MA remained unaltered even after 50,000 accelerated degradation test (ADT) cycles, which makes it a promising stable catalyst with its activity better than that of the state-of-the-art Pt/C. The undesired 2e– transfer ORR forming hydrogen peroxide (H2O2) is diminished in Pt0.2Pd1.8Ge as visible from the rotating ring-disk electrode (RRDE) experiment, spectroscopically visualized by in situ Fourier transform infrared (FTIR) spectroscopy and supported by computational studies. The effect of Pt substitution on Pd has been properly manifested by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The swinging of the oxidation state of atomic sites of Pt0.2Pd1.8Ge during the reaction is probed by in situ XAS, which efficiently enhances 4e– transfer, producing an extremely low percentage of H2O2.

Facile Solid-Phase Method for Preparing a Highly Active and Stable PtZn-Based Oxygen Reduction/Hydrogen Evolution Bifunctional Electrocatalyst: Effect of Bi-Facet Lattice Strain on Catalytic Activity

“…This higher energy implies a higher oxidation state of Pt, which is mainly due to surface oxidation tendency being exposed under ORR conditions. 49 At the same time, the Zn 2p XPS peaks did not shift significantly, indicating that catalyst degradation has not occurred after ADT cycles. Finally, d-PtZn/NC also exhibits competitive catalytic performance compared to the state-of-the-art ORR catalysts (Table S9).…”

“…0.2 eV) after post-ORR ADT testing. This higher energy implies a higher oxidation state of Pt, which is mainly due to surface oxidation tendency being exposed under ORR conditions . At the same time, the Zn 2p XPS peaks did not shift significantly, indicating that catalyst degradation has not occurred after ADT cycles.…”

Intermetallic Nanoarchitectures for Efficient Electrocatalysis

“…An in-depth operando analysis can reveal the reaction mechanism on the surface of intermetallic phases and guide the proper composition and structures of new intermetallic nanoarchitectures. For examples, Peter et al conducted operando Fourier transform infrared (FTIR) spectroscopy and computational studies to reveal reaction mechanisms of water formation during the ORR (Figure c) . They observed changes in the structure and reaction kinetics of the intermetallic Pt 0.2 Pd 1.8 Ge catalyst during electrocatalytic reactions and confirmed that inhibition of OH* poisoning was induced by weaker OH* adsorption and stronger OOH* adsorption.…”

Highly Efficient Hydroxyl Radicals Production Boosted by the Atomically Dispersed Fe and Co Sites for Heterogeneous Electro-Fenton Oxidation

“…The in situ FT-IR spectra are recorded by varying the potential stepwise from 0.4 to 0 V vs RHE in O 2 -saturated 0.1 mol L −1 Na 2 SO 4 solution (pH 6), and the in situ FT-IR spectrum (the gray curve) in the absence of the applied potential is recorded as the control. As shown in Figure 4a, the band at around 1419 cm −1 is attributed to the O−O stretching mode of adsorbed O 2 molecules on the CoFe DAC surface, 31 which is the prerequisite for ORR. Significantly, a main band at 1224 cm −1 and a weak band at 1387 cm −1 appear and increase with the negative shifting potential for CoFe DACs.…”