Elucidating the Formation and Structural Evolution of Platinum Single-Site Catalysts for the Hydrogen Evolution Reaction

Platinum-Grafted Twenty-Five Atom Gold Nanoclusters for Robust Hydrogen Evolution

A robust hydrogen evolution is demonstrated from Au25(PET)18]- nanoclusters (PET = 2-phenylethanethiol) grafted with minimal platinum atoms. The fabrication involves an electrochemical activation of nanoclusters by partial removal of thiols, without affecting the metallic core, which exposes Au-sites adsorbed with hydrogen and enables an electroless grafting of platinum. The exposed Au-sites feature the (111)-facet of the fcc-Au25 nanoclusters as assessed through lead underpotential deposition. The electrochemically activated nanoclusters (without Pt loading) show better electrocatalytic reactivity toward hydrogen evolution reaction than the pristine nanoclusters in an acidic medium. The platinum-grafted nanocluster outperformed with a lower overpotential of 0.117 V vs RHE (RHE = Reversible Hydrogen Electrode) compared to electrochemically activated nanoclusters (0.353 V vs RHE ) at 10 mA cm-2 and is comparable with commercial Pt/C. The electrochemically activated nanoclusters show better reactivity at higher current density owing to the ease of hydrogen release from the active sites. The modified nanoclusters show unique supramolecular self-assembly characteristics as observed in electron microscopy and tomography due to the possible metallophilic interactions. These results suggest that the post-surface modification of nanoclusters will be an ideal tool to address the sustainable production of green hydrogen.

Ultrafine Pt-based catalyst decorated with oxygenophilic Ni-sites accelerating alkaline H2O dissociation for efficient hydrogen evolution

Although Pt is a widely adopted commercial catalyst for the hydrogen evolution reaction (HER), its practical application is greatly limited by its prohibitive cost and high energy barrier for H2O dissociation in alkaline media. Herein, an ultrafine Pt-based catalyst decorated with oxygenophilic Ni-sites is rationally designed and successfully synthesized with Pt5(GS)10 (HGS = l-reduced glutathione) nanocluster precursor. The optimized Ni-decorated Pt catalyst (Ni-Pt-C-500) with ultrafine nanoparticles (about 1.6 nm) exhibits a low overpotential (14.0 mV) at 10 mA cm-2 and a mild Tafel slope of 20.8 mV dec-1 in the HER, which is superior to its undecorated counterpart (Pt-C-500), the commercial 20 wt% Pt/C catalyst and most of the previously reported Pt-based electrocatalysts. Experimental observations and theoretical calculations indicate that H2O could be spontaneously adsorbed to Ni-sites of the Ni-Pt-C-500 catalyst. Mechanistic studies reveal that Ni-sites promote HER by accelerating the kinetic of H2O cleavage and optimizing the electronic structure of Pt. This work paves a new avenue for designing other ultrafine hybrid electrocatalysts based on metal nanoclusters to enhance catalytic reaction kinetics.

Resonant Excitation Unlocks Chemical Selectivity of Platinum Lβ Valence-to-Core X-ray Emission Spectra

Valence-to-core X-ray emission spectroscopy (VtC XES) is an emerging technique that uses hard X-rays to probe the valence electronic structure of an absorbing atom. Despite finding varied applications for light elements and first row transition metals, little work has been done on heavier elements such as second and third row transition metals. This lack of application is at least partially due to the relatively low resolution of the data at the high energies required to measure these elements, which obscures the useful chemical information that can be extracted from the lower energy, higher resolution spectra of lighter elements. Herein, we collect data on a set of platinum-containing compounds and demonstrate that the VtC XES resolution can be dramatically enhanced by exciting the platinum atom in resonance with its L3-edge white line absorption. Whereas spectra excited using standard nonresonant absorption well above the Pt L3-edge display broad, unfeatured VtC regions, resonant XES (RXES) spectra have more than twofold improved resolution and are revealed to be rich in chemical information with the ability to distinguish between even closely related species. We further demonstrate that these RXES spectra may be used to selectively probe individual components of a mixture of Pt-containing compounds, establishing this technique as a viable probe for chemically complex samples. Lastly, it is shown that the spectra are interpretable using a molecular orbital framework and may be calculated using density functional theory, thus suggesting resonant excitation as a general strategy for extracting chemically useful information from heavy element VtC spectra.

Orange Peel Biomass-derived Carbon Supported Cu Electrocatalysts Active in the CO2 -Reduction to Formic Acid

We report a green, wet chemistry approach towards the production of C-supported Cu electrocatalysts active in the CO₂ reduction to formic acid. We use citrus peels as a C support precursor and as a source of reducing agents for the Cu cations. We show that orange peel is a suitable starting material compared to lemon peel for the one-pot hydrothermal synthesis of Cu nanostructures affording better Cu dispersion as well as productivity and selectivity towards formic acid. We rationalize this finding in terms of the beneficial chemical composition of the orange peel, which favors both the reduction of the Cu precursor as well as the carbon matrix. This work demonstrates new viable opportunities for the reuse of citrus waste on a rational basis.