Abnormal subsurface hydrogen diffusion behaviors in heterogeneous hydrogenation reactions

Screening of Carbon-Supported Platinum Electrocatalysts Using Frumkin Adsorption Isotherms

An important stage in the development of platinum electrocatalysts on carbon support is the analysis of their basic parameters. Cyclic voltammetry is an effective tool for analyzing the structural and electrochemical properties of such electrocatalysts. Using Frumkin adsorption isotherms, the contribution of the platinum surface to the hydrogen adsorption region was well described by three peaks corresponding to different crystal structures. The screening was carried out for platinum black and platinum electrocatalysts supported by carbon black, reduced graphene oxide (RGO), carbon nanotubes (CNTs), and nanofibers (CNFs). For most samples, the peak contribution to the electrochemical surface area (ESA) and corresponding hydrogen adsorption energies had close values, but the parameters deviated for Pt black and RGO-based samples was observed. The dependence of the calculated peak parameters on the number of accelerated stress test cycles was used to evaluate the effect of the type of carbon support on the stability of the electrocatalyst and the structure of platinum nanoparticles. The experimental results indicate a high degree of stability and differences in the degradation mechanisms of electrocatalysts based on nanostructured carbon compared to carbon black, which are explained by differences in the metal-support interaction and corrosion resistance of nanostructured carbon supports.

The role of sub-surface hydrogen on CO2 reduction and dynamics on Ni(110): An ab initio molecular dynamics study

The catalytic reduction in carbon dioxide is a crucial step in many chemical industrial reactions, such as methanol synthesis, the reverse water-gas shift reaction, and formic acid synthesis. Here, we investigate the role of bulk hydrogen, where hydrogen atoms are found deep inside a metal surface as opposed to subsurface ones, upon CO₂ reduction over a Ni(110) surface using density functional theory and ab initio molecular dynamics simulations. While it has previously been shown that subsurface hydrogen stabilizes CO₂ and can aid in overcoming reaction barriers, the role of bulk hydrogen is less studied and thus unknown with regard to CO₂ reduction. We find that the presence of bulk hydrogen can significantly alter the electronic structure of the Ni(110) surface, particularly the work function and d-band center, such that CO₂ adsorbs more strongly to the surface and is more easily reduced. Our results show an enhanced CO₂ dissociation in the presence of bulk hydrogen, shedding light on a hitherto underappreciated mechanistic pathway for CO₂ reduction on metal surfaces.

Hot-Atom Mechanism in Syngas Methanation on Precovered Pd(100) Surfaces

The excess energy of subsurface hydrogen species may facilitate overcoming reaction barriers and remarkably alters the reaction pathways. We present an in-depth study on the different reactivity of surface and subsurface hydrogen species in syngas methanation on the O/C-covered Pd(100) by using density functional theory calculations and microkinetic simulations. It is shown that the apparent energy barriers to form H₂O and CH₄ are reduced by 0.87 and 0.61 eV for the case in which the hot subsurface hydrogen species are involved in the whole hydrogenation process. The activity of O-covered Pd(100) is better than that of the C-covered surface, and the reactivity of subsurface hydrogen species is much higher than that of surface hydrogen species under ambient conditions. Increasing CO partial pressure strongly enhances the reactivity of subsurface hydrogen species in syngas methanation on the O-covered Pd(100). These important results are helpful for understanding the hot-atom mechanism through subsurface heterogeneous catalysis.