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The surfaces of nanomaterials with applications in optoelectronics and catalysis control their physicochemical properties. NMR spectroscopy, enhanced by dynamic nuclear polarization (DNP), is a powerful approach to probe the local environment of spin-1/2 nuclei near surfaces. However, this technique often lacks robustness and resolution for half-integer quadrupolar nuclei, which represent more than 66% of the NMR-active isotopes. A novel pulse sequence is introduced here to circumvent these issues. This method is applied to observe with high-resolution Al-27 and O-17 spin-5/2 nuclei on the surface of gamma-alumina. Moreover, we report high-resolution O-17 spectra of ZnO nanoparticles used in optoelectronics. Their assignment using DFT calculations allows the first NMR observation of vacancies near the surfaces. Finally, we employ the introduced NMR technique to observe B-11 spin-3/2 nuclei on the surface of partially oxidized boron nitride supported on silica and to distinguish its different BO2OH active sites.

One key process involving single atom catalysts (SACs) is the electroreduction of CO2 to fuels. The chemistry of SACs differs largely from that of extended catalytic surfaces, presenting an opportunity to improve the ability to activate very stable molecules, such as CO2. In this work, we performed a density functional theory (DFT) study of CO2 activation on a series of SACs, focusing on the role played by the adopted functional in activity predictions. The role of the exchange-correlation functional has been widely investigated in heterogenous catalysts, but it is less explored in SACs. We tested the widely used PBE and the PBE+U corrected functionals against the more robust hybrid PBE0 functional. The results show that PBE is reliable if one is interested in qualitative predictions, but it leads to some inaccuracies in other cases. A possible way to attenuate this effect is by adopting the PBE+U framework, as it gives results that are very similar to PBE0 at an acceptable computational cost. The results of this study further underline the importance of the computational framework adopted in predicting the activity of SACs. The work suggests that one needs to go beyond PBE for quantitative estimates, an important consideration when performing screening and high-throughput calculations.

N-Heterocyclic olefins (NHOs), possessing highly polarizable and remarkably electron-rich double bonds, have been effectively utilized as exceptional anchors for surface modifications. Herein, the adsorption, orientation, and electronic properties of NHOs on a metal surface are investigated. On Cu(111), the sterically low-demanding IMe-NHO is compared to its analogous IMe-NHC counterpart. High-resolution electron energy-loss spectroscopy (HREELS) measurements show for both molecules a flat-lying ring adsorption configuration. While the NHC adopts a dimer configuration including a Cu adatom, the NHO chemisorbs over a C–Cu bond perpendicular to the surface. This distinct difference leads for the IMe-NHOs to have a higher thermal stability on the surface. Moreover, IMe-NHOs introduce a higher net electron transfer to the surface compared to the IMe-NHCs, which results in a stronger effect on the work function. These results highlight the role of NHOs in surface science as they extend the functionalization capabilities of NHCs into stronger electronic modification.

The attention toward single-atom catalysts (SACs) for electrochemical processes is growing at an impressive pace. Electronic structure calculations play an important role in this race by providing proposals of potentially relevant catalysts based on screening studies or on the identification of descriptors of the chemical activity. So far, almost all of these predictions ignore a crucial aspect in the design of a catalyst: its stability. We propose a simple yet general first-principles approach to predict the stability of SACs under working conditions of pH and applied voltage. This is based on the construction of a thermodynamic cycle, where part of the information is taken from experiment and the rest from density functional theory (DFT) calculations. In particular, we make use of the formalism of Pourbaix diagrams to investigate the stability of SACs in reductive or oxidative conditions and we identify those that show a pronounced tendency to dissolve or to form other chemical species. Applying the procedure to four transition metal atoms, Cr, Mn, Fe, and Co, and to three supports, N-doped graphene, carbon nitride, and covalent organic frameworks, we show that a key factor in determining the final stability is the binding energy of the free metal atom to the support. The results show that several potentially very good catalysts in key electrochemical reactions are, in fact, dramatically prone to dissolution or transformation in other chemical species, suggesting that every prediction of the SAC’s catalytic activity should be accompanied by a parallel investigation of the stability.

Single atom catalysis is relatively new frontier in catalysis with potential application in several critical chemical processes, such as water splitting reactions. Single atom catalysts (SACs) are analogues of coordination chemistry compounds, opening the way to the formation of unconventional intermediates compared to extended metal or oxide catalyst surfaces. In this work we show by means of density functional theory (DFT) calculations that the formation of unconventional adsorbates on SACs in the oxygen evolution reaction (OER) leads to complex scaling relationships, that differ from the scaling relations observed on extended surfaces. The evidence of new scaling relations directly impacts the expected catalytic activity and provides a further example of the importance of including in the modelling species beyond those that form on classical electrodes.

A computational screening of Single Atom Catalysts (SACs) bound to titanium nitride (TiN) is presented, for the Hydrogen Evolution Reaction (HER), based on density functional theory. The role of fundamental ingredients is explored to account for a reliable screening of SACs. Namely, the formation of H2-complexes besides the classical H* one impacts the predicted HER activity, in line with previous studies on other SACs. Also, the results indicate that one needs to adopt self-interaction-corrected functionals. Finally, predicting an active catalyst is of little help without an assessment of its stability. Thus, it is included in the theoretical framework the analysis of the stability of the SACs in working conditions of pH and voltage. Once unconventional intermediates and stability are considered in a self-interaction corrected scheme, the number of potential good catalysts for HER is strongly reduced since i) some potentially good catalysts are not stable against dissolution and ii) the formation of unconventional intermediates leads to thermodynamic barriers. This study highlights the importance of including ingredients for the prediction of new systems, such as the formation of unconventional intermediates, estimating the stability of SACs, and the adoption of self-interaction corrected functionals. Also, this study highlights some interesting candidates deserving of dedicated work.

Cross-coupling reactions are of great importance in chemistry due to their ability to facilitate the construction of complex organic molecules. Among these reactions, the Ullmann-type C−O coupling between phenols and aryl halides is particularly noteworthy and useful for preparing diarylethers. However, this reaction typically relies on homogeneous catalysts that rapidly deactivate under harsh reaction conditions. In this study, we introduce a novel heterogeneous catalyst for the Ullmann-type C−O coupling reaction, comprised of isolated Cu atoms chelated to a tetraethylenepentamine-pyrrole ligand that is immobilized on graphite nanoplatelets. The catalytic study reveals the recyclability of the material, and demonstrates the crucial role of the pyrrole linker in stabilizing the Cu sites. The work expands the potential of single-atom catalyst nanoarchitectures and underscores the significance of ligands in stabilizing metals in cationic forms, providing a novel, tailored catalyst for cross-coupling chemistries.

For more than half a century, the industrial production of methanol in the world has been based on a heterogeneous Cu/ZnO/Al2O3 catalyst where Cu nanoparticles are dispersed on an alumina support with ZnO particles as promoters. The reaction starts with syngas, a mixture of CO, CO2, and hydrogen, and the hydrogenation of carbon dioxide is an essential part of the process. Despite the technological importance and the high number of studies dedicated to identifying the structure of the functioning catalyst, there are still several open questions on the nature of the active sites and phases. Over the years, various hypotheses have been formulated. The most accredited versions concern the formation of CuZn alloys, the migration of ZnO over the Cu nanoparticles which become covered by an ultrathin oxide layer, and the role of the Cu-ZnO interface and, in particular, of the presence of Cu+ ions. The role of alumina as a promoter has also been widely discussed, suggesting that the oxide provides acidic sites where intermediates are stabilized or that Al dopants enter the ZnO phase, altering its properties. The reality, as discussed in this brief overview, is that all these mechanisms are probably contributing but under different conditions of temperature, pressure, and reagent composition. This results in a dynamic catalyst that makes unambiguous identification of active sites difficult, if not impossible. Less controversial is the reaction mechanism, although even in this case the path followed by the reaction is a delicate function of various conditions, including the composition of the reaction mixture and the presence of water or other contaminants.

This work evaluates the feasibility of alkaline hydrogen evolution reaction (HER) using Pt single-atoms (1.0 wt %) on defect-rich ceria (Pt1/CeOx) as an active and stable dual-site catalyst. The catalyst displayed a low overpotential and a small Tafel slope in an alkaline medium. Moreover, Pt1/CeOx presented a high mass activity and excellent durability, competing with those of the commercial Pt/C (20 wt %). In this picture, the defective CeOx is active for water adsorption and dissociation to create H* intermediates, providing the first site where the reaction occurs. The H* intermediate species then migrate to adsorb and react on the Pt2+ isolated atoms, the site where H2 is formed and released. DFT calculations were also performed to obtain mechanistic insight on the Pt1/CeOx catalyst for the HER. The results indicate a new possibility to improve the state-of-the-art alkaline HER catalysts via a combined effect of the O vacancies on the ceria support and Pt2+ single atoms.

RuO2 and IrO2 are among the most active catalysts for the Oxygen Evolution Reaction (OER). Recently, it was demonstrated that the catalytic surface of these oxides plays a role in the reaction, where a hydrogen bond with a neighbor OH group stabilizes an unconventional −OO intermediate (−OO–H), prior to O2 evolution. Quantum chemical calculations neglecting solvation effects indicated that this intermediate is more stable than the conventional −OOH, and that deprotonation of the stabilizing −OH is the rate limiting step for OER on RuO2(110) and RuO2(100). In this work, we investigate the role of water molecules on the relative stability of −OOH and −OO–H oxygenates on RuO2 (110) by means of density functional theory calculations combined with ab initio Molecular Dynamics simulations (AIMD). We show that the two intermediates participate in a hydrogen bonding network with water to a similar extent, but leading to different interfacial water structures, with possible implications on interfacial proton dynamics and reaction kinetics. Moreover, −OOH can spontaneously convert to −OO–H through a process mediated by water, demonstrating the critical role of explicitly including water in the model. This study provides further mechanistic insights on the role of the oxide surface chemistry in the OER mechanism and highlights the importance of explicitly treating the catalyst/water interfaces including dynamical aspects to assess the stability and the interconversion mechanism of key surface species, since the adoption of static solvation approaches tends to overestimate the energetic difference between −OOH and −OO–H reaction intermediates.