Roberto Félix

High-entropy oxides retain a significantly larger population of oxygen vacancies (OVs) compared to their single-element or binary metal oxide counterparts, highlighting their unique potential as prospective electrocatalytic materials. However, the stabilization of surface oxygen vacancies (S-OVs) is highly challenging due to their inherently dynamic nature generally resulting in defect healing, migration, or initiation of structural collapse under operating conditions. By means of rational high-throughput materials science, we investigate the stability of S-OVs in (Cu-Fe-Ni-Cr-Zn)O _x high-entropy oxides covering a compositional search space of at least 5 to 35 %. A methodology based on X-ray photoelectron spectroscopy and X-ray absorption spectroscopy is utilized to quantitatively follow the distribution of the OVs across the materials library. For low Zn stoichiometries, (Cu ₁₄ -Fe ₁₃ -Ni ₅ -Cr ₈ -Zn ₄ )O ₅₅ , complete stabilization of S-OVs is achieved even after prolonged exposure to ambient environment. The discovery of S-OV stabilization in our high-entropy oxide system is a prerequisite to exploit the unique properties of this class of materials for electrocatalytic applications and beyond.

The performance of perovskite solar cells (PSCs) is critically dependent on the quality of interfaces and grain boundaries, which often lead to nonradiative recombination losses, degradation, and inefficient charge transport. Here, we introduce an asymmetric bulky cation with a dipole moment (2.48 Debye), 4‐methoxyphenethylammonium bromide (MPB), at the perovskite/hole transport layer (HTL) interface in planar (n‐i‐p) PSCs. The MPB provides dual functionality, not only as a defect passivation agent for undercoordinated Pb ²⁺ but also improving charge extraction at the perovskite/HTL interface. The MPB‐passivated PSCs exhibit enhanced crystallinity and an increase in hole‐carrier diffusion length (from 540 to 770 nm). We quantitatively attributed the built‐in potential increase (from 1.09 ± 0.01 to 1.12 ± 0.01 V) to a larger charge‐carrier driving force in MPB‐treated devices, as determined by Mott–Schottky analysis. The optimized PSCs achieve a higher power‐conversion efficiency (PCE) of 22.7% compared to the control device (PCE of 21.5%). Consequently, the MPB‐treated device retained 80% of its initial PCE, compared with 60% for the control, under standard illumination, ~35% relative humidity (RH), and a temperature of ~45 °C after 2000 s. This work provides valuable insights into defect passivation through dipole‐assisted molecular interface engineering, which enhances charge extraction and overall device performance, offering a pathway for high‐efficiency PSCs.

Molybdenum supported on a H-Beta 150 zeolite was studied in the conversion of dimethyl ether (DME) to a sustainable chemical equivalent for conventional liquified petroleum gas (LPG). Catalysts with varying Mo loadings (1 to 20 wt.-%) were compared to the bare zeolite and an Pd/H-Beta 150 catalyst. Low Mo loadings (1 and 5 wt.-%) enhance LPG selectivity and hydrogenation activity, while the higher loadings (10 and 20 wt.-%) induce pore blockage and reduce activity significantly. The 5 wt.-% Mo species/H-Beta 150 catalyst exhibit the best balance of high selectivity and moderate olefin to paraffin ratio. Operating conditions were evaluated and revealed that higher temperatures increase DME conversion but favoured CO, CO2, and methane formation. These findings suggest that Mo/H-Beta 150 catalysts provide a viable, cost-effective alternative to platinum group metals based catalysts for the selective production of LPG from DME.

Interfacial phenomena critically influence both the performance and long-term stability of perovskite solar cells; hence, optimizing interfaces remains a key challenge for their commercialization. In this study, we investigate the chemical interactions and electronic structure of the buried interface between the FAPbI₃ perovskite absorber and spiro-OMeTAD-based hole transport layer (HTL) in an ITO/SnO₂/FAPbI₃/HTL device using hard X-ray photoelectron spectroscopy. Our results indicate Pb and I ion incorporation in the spiro-OMeTAD HTL. The Pb 4f core level spectra show the formation of new nonperovskite Pb species, and the N 1s spectra exhibit an additional peak, indicating chemical modifications induced by the deposition of spiro-OMeTAD on the perovskite layer. Moreover, the spiro-OMeTAD N 1s peak exhibits a systematic shift toward lower binding energies with increasing HTL thickness, indicating a downward band bending in the spiro-OMeTAD HTL. Overall, these findings provide direct insight into the chemical and electronic interactions near the FAPbI₃/HTL interface and emphasize the importance of optimizing transport layer thickness to achieve favorable energy level alignment and improved device performance.

Amorphous hydrous iridium oxide thin films (am-hydr-IrO _x ) grown through electrochemical treatment of sputtered iridium thin films are an interesting class of materials for the oxygen evolution reaction (OER).

A new electrochemical metric quantifies detrimental redox activity in nickel oxide hole transport layers, directly linking surface reactivity to solar cell efficiency and guiding targeted passivation for stable, high-performance photovoltaics.

A phosphate modification strategy enhances the dispersion and thermal stability of Pd nanoparticles supported on Al ₂ O ₃ , while enabling efficient aromatic hydrogenation under hydrogen streams containing CO impurities.