Nitrogen-doped carbon materials featuring atomically dispersed metal cations (M−N−C) are an emerging family of materials with potential applications for electrocatalysis. The electrocatalytic activity of M−N−C materials toward four-electron oxygen reduction reaction (ORR) to H 2 O is a mainstream line of research for replacing platinumgroup-metal-based catalysts at the cathode of fuel cells. However, fundamental and practical aspects of their electrocatalytic activity toward two-electron ORR to H 2 O 2 , a future green "dream" process for chemical industry, remain poorly understood. Here we combined computational and experimental efforts to uncover the trends in electrochemical H 2 O 2 production over a series of M−N−C materials (M = Mn, Fe, Co, Ni, and Cu) exclusively comprising atomically dispersed M−N x sites from molecular first-principles to bench-scale electrolyzers operating at industrial current density. We investigated the effect of the nature of a 3d metal within a series of M−N−C catalysts on the electrocatalytic activity/selectivity for ORR (H 2 O 2 and H 2 O products) and H 2 O 2 reduction reaction (H 2 O 2 RR). Co−N−C catalyst was uncovered with outstanding H 2 O 2 productivity considering its high ORR activity, highest H 2 O 2 selectivity, and lowest H 2 O 2 RR activity. The activity−selectivity trend over M−N−C materials was further analyzed by density functional theory, providing molecular-scale understandings of experimental volcano trends for four-and two-electron ORR. The predicted binding energy of HO* intermediate over Co−N−C catalyst is located near the top of the volcano accounting for favorable two-electron ORR. The industrial H 2 O 2 productivity over Co−N−C catalyst was demonstrated in a microflow cell, exhibiting an unprecedented production rate of more than 4 mol peroxide g catalyst −1 h −1 at a current density of 50 mA cm −2 .
This 2007 Chemistry Nobel prize update covers scientific advances of the past decade in our understanding of electrocatalytic processes on surfaces of nanoscale shape-controlled polyhedral solids. It is argued that the field of chemical reaction processes on solid surfaces has recently been paying increasing attention to the fundamental understanding of electrified solid-liquid interfaces and toward the operando study of the minute fraction of catalytically active, structurally dynamic non-equilibrium Taylor-type surface sites. Meanwhile, despite mounting evidence of acting as structural proxies in some cases, the concept of catalytic structure sensitivity of well-defined nanoscale solid surfaces continues to be a key organizing principle for the science of shape-controlled nanocrystals and, hence, constitutes a central recurring theme in this review. After addressing key aspects and recent progress in the wet-chemical synthesis of shaped nanocatalysts, three areas of electrocatalytic processes on solid shape-controlled nanocrystals of current scientific priority are discussed in more detail: the oxygen electroreduction on shape-controlled Pt-Ni polyhedra with its technological relevance for low temperature fuel cells, the CO electroreduction to hydrocarbons on Cu polyhedra and the puzzling interplay between chemical and structural effects, and the electrocatalytic oxygen evolution reaction from water on shaped transition metal oxides. The review closes with the conclusion that Surface Science and thermal catalysis, honored by Ertl's Nobel prize a decade ago, continue to show major repercussions on the emerging field of Interface Science.
We report on the salt-induced aggregation of citrate-coated gold nanoparticles (AuNPs) confined within poly(N-isopropylacrylamide) (PNIPAM) brushes grafted from flat substrates. Compared to highly dispersed AuNPs, a red-shift and broadening of the surface plasmon (SP) band is observed when the AuNPs are confined by the PNIPAM brush matrix due to their close vicinity. Additional red-shifting and broadening occur upon immersion in aqueous salt solutions (1 M NaF, NaCl, NaBr, and KCl). Nanoparticle assemblies are established due to salt-induced aggregation of AuNPs and are dependent on the type of salt. In the presence of KCl, nanoparticle assemblies are built up that result in the formation a second plasmon peak at ∼700 nm. The color change of PNIPAM/AuNP is associated with (1) the collapse of the PNIPAM brushes in the presence of salt and (2) nanoparticle aggregation due to electrostatic screening of the negative charges around the AuNPs by the salt ions. Ion specificity is related to ion-pair association energies and adsorption behavior of ions at the AuNP surface. In addition, we perform a neutron reflectivity experiment to resolve the internal structure of swollen PNIPAM/AuNP hybrids and find that penetrated AuNPs cause PNIPAM chain stretching due to electrostatic repulsion between charged particles in the brush.
Peptidylprolyl isomerase cyclophilins play critical roles in a variety of biological processes. Recent findings that cyclophilins are present at high levels in the CNS and that cyclosporin A may possess neuroprotective/neurotrophic effects have prompted us to search for nonimmunosuppressant small molecule cyclophilin ligands. To this end, we report the lead identification through "virtual screening" and the synthesis of our first series of non-peptidic cyclophilin ligands, along with the preliminary biological results.
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