Self-Assembly Intermetallic PtCu3 Core with High-Index Faceted Pt Shell for High-Efficiency Oxygen Reduction.

Rational design of well-defined active sites is crucial for promoting sluggish oxygen reduction reactions. Herein, leveraging the surfactant-oriented and solvent-ligand effects, we develop a facile self-assembly strategy to construct a core-shell catalyst comprising a high-index Pt shell encapsulating a PtCu3 intermetallic core with efficient oxygen-reduction performance. Without undergoing a high-temperature route, the ordered PtCu3 is directly fabricated through the accelerated reduction of Cu2+, followed by the deposition of the remaining Pt precursor onto its surface, forming high-index steps oriented by the steric hindrance of surfactant. This approach results in a high half-wave potential of 0.911 V versus reversible hydrogen electrode, with negligible deactivation even after 15000-cycle operation. Operando spectroscopies identify that this core-shell catalyst facilitates the conversion of oxygen-involving intermediates and ensures antidissolution ability. Theoretical investigations rationalize that this improvement is attributed to reinforced electronic interactions around high-index Pt, stabilizing the binding strength of rate-determining OHads species.

Uncovering Structural Evolution during the Dealloying Process in Pt-Based Oxygen-Reduction Catalyst.

The comprehensive understanding toward the dealloying process is crucial for designing alloy catalysts employed in the oxygen reduction reaction (ORR). However, the specific leaching procedure and subsequent reconstruction of the dealloyed catalyst still remain unclear. Herein, we employ in situ X-ray absorption fine structure spectroscopy to monitor the dealloying process of a two-dimensional PtTe ordered alloy, known for its enhanced ORR activity. Our findings reveal the unsynchronous evolutions of Pt and Te sites, wherein the Pt component undergoes a structural transformation prior to the complete leaching of Te, leading to the formation of a defect-rich Pt catalyst. This dealloyed catalyst exhibits a significant enhancement in ORR activity, featuring a half-wave potential of 0.90 V versus the reversible hydrogen electrode and a mass activity of 0.62 A mgPt-1, outperforming the performance of commercial Pt/C counterpart. This in-depth understanding of the dealloying mechanism enriches our knowledge for the development of high-performance Pt-based alloy catalysts.

Identification of K+-determined reaction pathway for facilitated kinetics of CO2 electroreduction.

Cations such as K+ play a key part in the CO2 electroreduction reaction, but their role in the reaction mechanism is still in debate. Here, we use a highly symmetric Ni-N4 structure to selectively probe the mechanistic influence of K+ and identify its interaction with chemisorbed CO2-. Our electrochemical kinetics study finds a shift in the rate-determining step in the presence of K+. Spectral evidence of chemisorbed CO2- from in-situ X-ray absorption spectroscopy and in-situ Raman spectroscopy pinpoints the origin of this rate-determining step shift. Grand canonical potential kinetics simulations - consistent with experimental results - further complement these findings. We thereby identify a long proposed non-covalent interaction between K+ and chemisorbed CO2-. This interaction stabilizes chemisorbed CO2- and thus switches the rate-determining step from concerted proton electron transfer to independent proton transfer. Consequently, this rate-determining step shift lowers the reaction barrier by eliminating the contribution of the electron transfer step. This K+-determined reaction pathway enables a lower energy barrier for CO2 electroreduction reaction than the competing hydrogen evolution reaction, leading to an exclusive selectivity for CO2 electroreduction reaction.