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  1. This study demonstrates an atomic composition manipulation on Pt–Ni nano-octahedra to enhance their electrocatalytic performance. By selectively extracting Ni atoms from the {111} facets of the Pt–Ni nano-octahedra using gaseous carbon monoxide at an elevated temperature, a Pt-rich shell is formed, resulting in an ∼2 atomic layer Pt-skin. The surface-engineered octahedral nanocatalyst exhibits a significant enhancement in both mass activity (∼1.8-fold) and specific activity (∼2.2-fold) toward the oxygen reduction reaction compared with its unmodified counterpart. After 20,000 potential cycles of durability tests, the surface-etched Pt–Ni nano-octahedral sample shows a mass activity of 1.50 A/mgPt, exceeding the initial mass activity of the unetched counterpart (1.40 A/mgPt) and outperforming the benchmark Pt/C (0.18 A/mgPt) by a factor of 8. DFT calculations predict this improvement with the Pt surface layers and support these experimental observations. This surface-engineering protocol provides a promising strategy for developing novel electrocatalysts with improved catalytic features. 
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  2. Electrocatalytic hydrogen evolution reaction (HER) is critical for green hydrogen generation and exhibits distinct pH-dependent kinetics that have been elusive to understand. A molecular-level understanding of the electrochemical interfaces is essential for developing more efficient electrochemical processes. Here we exploit an exclusively surface-specific electrical transport spectroscopy (ETS) approach to probe the Pt-surface water protonation status and experimentally determine the surface hydronium pK a = 4.3. Quantum mechanics (QM) and reactive dynamics using a reactive force field (ReaxFF) molecular dynamics (RMD) calculations confirm the enrichment of hydroniums (H 3 O + * ) near Pt surface and predict a surface hydronium pK a of 2.5 to 4.4, corroborating the experimental results. Importantly, the observed Pt-surface hydronium pK a correlates well with the pH-dependent HER kinetics, with the protonated surface state at lower pH favoring fast Tafel kinetics with a Tafel slope of 30 mV per decade and the deprotonated surface state at higher pH following Volmer-step limited kinetics with a much higher Tafel slope of 120 mV per decade, offering a robust and precise interpretation of the pH-dependent HER kinetics. These insights may help design improved electrocatalysts for renewable energy conversion. 
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  3. A recent advance in the synthesis of alkenylated arenes was the demonstration that the Pd(OAc)2 catalyst precursor gives >95% selectivity toward styrene from ethylene and benzene under optimized conditions using excess Cu(II) carboxylate as the in situ oxidant [ Organometallics 2019, 38(19), 3532−3541]. To understand the mechanism underlying this catalysis, we applied density functional theory (DFT) calculations in combination with experimental studies. From DFT calculations, we determined the lowest-energy multimetallic Pd and Pd–Cu mixed metal species as possible catalyst precursors. From the various structures, we determined the cyclic heterotrinuclear complex PdCu2(μ-OAc)6 to be the global minimum in Gibbs free energy under conditions of excess Cu(II). For cyclic PdCu2(μ-OAc)6 and the parent [Pd(μ-OAc)2]3, we evaluated the barriers for benzene C–H activation through concerted metalation deprotonation (CMD). The PdCu2(μ-OAc)6 cyclic trimer leads to a CMD barrier of 33.5 kcal/mol, while the [Pd(μ-OAc)2]3 species leads to a larger CMD barrier at >35 kcal/mol. This decrease in the CMD barrier arises from the insertion of Cu(II) into the trimetallic species. Because cyclic PdCu2(μ-OAc)6 is likely the predominant species under experimental conditions (the Cu to Pd ratio is 480:1 at the start of catalysis) with a predicted CMD barrier within the range of the experimentally determined activation barrier, we propose that cyclic PdCu2(μ-OAc)6 is the Pd species responsible for catalysis and report a full reaction mechanism based on DFT calculations. For catalytic conversion of benzene and ethylene to styrene at 120 °C using Pd(OAc)2 as the catalyst precursor and Cu(OPiv)2 (OPiv = pivalate) as the oxidant, an induction period of ∼1 h was observed, followed by catalysis with a turnover frequency of ∼2.3 × 10–3 s–1. In situ1H NMR spectroscopy experiments indicate that during the induction period, Pd(OAc)2 is likely converted to cyclic PdCu2(η2-C2H4)3(μ-OPiv)6, which is consistent with the calculations and consistent with the proposal that the active catalyst is the ethylene-coordinated heterotrinuclear complex cyclic PdCu2(η2-C2H4)3(μ-OPiv)6. 
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