A combination of N 1s X-ray photoelectron spectroscopy (XPS) and first principles calculations of nitrogen-containing model electrocatalysts was used to elucidate the nature of the nitrogen defects that contribute to the binding energy (BE) range of the N 1s XPS spectra of these materials above ∼400 eV. Experimental core level shifts were obtained for a set of model materials, namely N-doped carbon nanospheres, Fe–N–carbon nanospheres, polypyrrole, polypyridine, and pyridinium chloride, and were compared to the shifts calculated using density functional theory. The results confirm that the broad peak positioned at ∼400.7 eV in the N 1s XPS spectra of N-containing catalysts, which is typically assigned to pyrrolic nitrogen, contains contributions from other hydrogenated nitrogen species such as hydrogenated pyridinic functionalities. Namely, N 1s BEs of hydrogenated pyridinic-N and pyrrolic-N were calculated as 400.6 and 400.7 eV, respectively, using the Perdew–Burke–Ernzerhof exchange-correlation functional. A special emphasis was placed on the study of the differences in the XPS imprint of N-containing defects that are situated in the plane and on the edges of the graphene sheet. Density functional theory calculations for BEs of the N 1s of in-plane and edge defects show that hydrogenated N defects are more sensitive to the change in the chemical environment in the carbon matrix than the non-hydrogenated N defects. Calculations also show that edge-hydrogenated pyridinic-N and pyrrolic-N defects only contribute to the N 1s XPS peak located at ∼400.7 eV if the graphene edges are oxygenated or terminated with bare carbon atoms.

Platinum‐based catalytic materials have received significant attention, particularly in the shape and size control of faceted materials for catalysis. More recently, there has been a rapid increase in the number of reports of successful preparations in this field; however, a fundamental understanding of controlled growth towards catalytic material design is essential for future implementation and broad application. In this review, we provide an overview of the recent findings reported since 2009, focusing on methods for shape control as well as the effects of exposed surface facets on select catalytic reactions. Copyright © 2013 John Wiley & Sons, Ltd.

Interactions at the gas−solid interface drive physicochemical processes in many energy and environmental applications; however, the challenges associated with characterization and development of these dynamic interactions in complex systems limit progress in developing effective materials. Therefore, structure−property−performance correlations greatly depend on the development of advanced techniques and analysis methods for the investigation of gas−solid interactions. In this work, adsorption behavior of O 2 and humidified O 2 on nitrogen-functionalized carbon (N−C) materials was investigated to provide a better understanding of the role of nitrogen species in the oxygen reduction reaction (ORR). N−C materials were produced by solvothermal synthesis and N-ion implantation, resulting in a set of materials with varied nitrogen amount and speciation in carbon matrices with different morphologies. Adsorption behavior of the N−C samples was characterized by in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS) experiments. A new analysis method for the interpretation of AP-XPS data was developed, allowing both the determination of overall adsorption behavior of each N−C material and identification of which nitrogen species were responsible for adsorption. The complementary information provided by in situ DRIFTS and AP-XPS indicates that O 2 adsorption primarily takes place on either electron-rich nitrogen species like pyridine, hydrogenated nitrogen species, or graphitic nitrogen. Adsorption of O 2 and H 2 O occurs competitively on solvothermally prepared N−Cs, whereas adsorption of H 2 O and O 2 occurs at different sites on N-ion implanted N−Cs, highlighting the importance of tuning the composition of N−C materials to promote the most efficient ORR pathway.

The design and synthesis of shape-directed nanoscale noble metal particles have attracted much attention due to their enhanced catalytic properties and the opportunities to study fundamental aspects of nanoscale systems. As such, numerous methods have been developed to synthesize crystals with tunable shapes, sizes, and facets by adding foreign species that promote or restrict growth on specific sites. Many hypotheses regarding how and why certain species direct growth have been put forward, however there has been no consensus on a unifying mechanism of nanocrystal growth. Herein, we develop and demonstrate the capabilities of a mathematical growth model for predicting metal nanoparticle shapes by studying a well known procedure that employs AgNO3 to produce {111} faceted Pt nanocrystals. The insight gained about the role of auxiliary species is then utilized to predict the shape of Pd nanocrystals and to corroborate other shape-directing syntheses reported in literature. The fundamental understanding obtained herein by combining modeling with experimentation is a step toward computationally guided syntheses and, in principle, applicable to predictive design of the growth of crystalline solids at all length scales (nano to bulk).