Elucidation of Structure–Activity Relations in Proton Electroreduction at Pd Surfaces: Theoretical and Experimental Study

Abstract

The structure–activity relationship is a cornerstone topic in catalysis, which lays the foundation for the design and functionalization of catalytic materials. Of particular interest is the catalysis of the hydrogen evolution reaction (HER) by palladium (Pd), which is envisioned to play a major role in realizing a hydrogen‐based economy. Interestingly, experimentalists observed excess heat generation in such systems, which became known as the debated “cold fusion” phenomenon. Despite the considerable attention on this report, more fundamental knowledge, such as the impact of the formation of bulk Pd hydrides on the nature of active sites and the HER activity, remains largely unexplored. In this work, classical electrochemical experiments performed on model Pd(hkl) surfaces, “noise” electrochemical scanning tunneling microscopy (n‐EC‐STM), and density functional theory are combined to elucidate the nature of active sites for the HER. Results reveal an activity trend following Pd(111) > Pd(110) > Pd(100) and that the formation of subsurface hydride layers causes morphological changes and strain, which affect the HER activity and the nature of active sites. These findings provide significant insights into the role of subsurface hydride formation on the structure–activity relations toward the design of efficient Pd‐based nanocatalysts for the HER.

Hydrogen Trapping in Palladium Nanoparticles Revealed by Electrochemical, X-ray Scattering, and Spectrometric Measurements

“…38 Schmidt et al have also recently shown that expansion of the Pd lattice leads to weaker adsorption energy of adsorbed H, enhancing the hydrogen evolution reaction rate in acidic medium. 39 ■ CONCLUSIONS In summary, our results shed fundamental light on the loss of H sorption capacity of Pd/C nanoparticles during repeated H insertion/de-insertion cycles. By combining electrochemistry and wide-angle X-ray scattering, we demonstrated that H atoms get progressively trapped in the Pd lattice.…”

“…For example, PdH 0.43 NPs were shown to be more active for methanol oxidation reaction compared to the pure metal Pd counterparts . Schmidt et al have also recently shown that expansion of the Pd lattice leads to weaker adsorption energy of adsorbed H, enhancing the hydrogen evolution reaction rate in acidic medium …”

Elucidating the Active Sites and Synergies in Water Splitting on Manganese Oxide Nanosheets on Graphite Support

“…A lower amplitude and a larger full width at half maximum in OER ‘On’ than in OER ‘Off’ correspond to a higher distribution of derivative slopes and, therefore, to a higher activity. A more detailed explanation of this evaluation technique is available in the Methods Section and in references [ 49 ] and [ 53 ] . A white square in Figure S7a in the Supporting Information highlights the position of the evaluated area.…”

Combining impedance and hydrodynamic methods in electrocatalysis. Characterization of Pt(pc), Pt5Gd, and nanostructured Pd for the hydrogen evolution reaction

“…EIS and RDE techniques were performed using a VSP-300 potentiostat (Bio-Logic, France). Since the EIS measurements were performed at high frequencies, measurement artifacts caused by the impedance of the RE were suppressed by a shunt capacitor placed between the RE and a Pt wire, which was immersed into the electrolyte close to the Luggin capillary [27,33]. This is also how to make the iR compensation for the HER/HOR polarization curves.…”

“…[22][23][24][25][26]). Finally, we used Pd nanoparticles supported on high surface area carbon (Pd/C) as a promising hydrogen evolution electrocatalyst to demonstrate the informative power of the EIS-RDE approach for a more complex system [27,28]. To harvest results with profound physical meaning, a suitable equivalent electric circuit (EEC) model for the EIS data is used in this work [19].…”