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.

Modulating the Electronic Structure of RuO2 through Cr Solubilizing for Improved Oxygen Evolution Reaction.

Hydrogen production from water electrolysis is important for the sustainable development of hydrogen energy. Nevertheless, the naturally torpid property of anodic oxygen evolution reaction (OER) kinetics and poor stability of its catalysts significantly restrict the development of electrochemical water splitting. Here, a Ru0.6 Cr0.4 O2 electrocatalyst is synthesized, which reveals excellent OER activity with the overpotential of only 195 mV at 10 mA cm-2 and excellent stability with the potential increase of merely 5.3 mV after 20 h continuous OER test in acidic media. Theoretical calculations reveal that the solubilizing of Cr into RuO2 could adjust the electron distribution, making the d-band center of Ru far away from the Fermi level. This behavior reduces the binding energy with Ru and O and accelerates the rate-determining step of OER (i.e., the formation of *OOH), thereby increasing OER activity. In addition, the incorporation of Cr increases the energy of oxygen defect formation and reduces the participation of lattice oxygen, thus improving the stability of the catalyst. This research furnishes a feasible policy for the development of highly active and stable catalysts in acidic media by regulating the electronic structure of RuO2 .

Experimental and Theoretical Solid-State 29Si NMR Studies on Defect Structures in La9.33+x(SiO4)6O2+1.5x Apatite Oxide Ion Conductors.

Oxide ion conductors can be used as electrolytes in solid oxide fuel cells, a promising energy-conversion technology. Local structures around the defects in oxide ion conductors are key for understanding the defect stabilization and migration mechanisms. As the defect contents are generally low, it is rather difficult to characterize the defect structure and therefore elucidate how oxide ions migrate. Solid-state nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for probing the local structures. However, the interpretation of NMR signals mainly based on the empirical knowledge could lead to unprecise local structures. There is still controversy regarding the defect structures in the apatite-type interstitial oxide ion conductors containing isolated tetrahedral units. Here, we combine the experimental solid-state 29Si NMR spectroscopy with theoretical density functional theory calculations to investigate the defect structures in La9.33+x(SiO4)6O2+1.5x apatites. The results indicate that the 29Si resonance signals on the high field side of the main peak corresponding to the Si atoms in the bulk structure are related to La vacancies and there is no steady-state SiO5 in the defect structures. This finding provides new atomic-level understanding to the stabilization and migration of interstitial oxide ions in silicate apatites, which could guide the design and discovery of new solid oxide fuel cell electrolyte materials.

Modulated structure determination and ion transport mechanism of oxide-ion conductor CeNbO4+δ.

CeNbO4+δ, a family of oxygen hyperstoichiometry materials with varying oxygen content (CeNbO4, CeNbO4.08, CeNbO4.25, CeNbO4.33) that shows mixed electronic and oxide ionic conduction, has been known for four decades. However, the oxide ionic transport mechanism has remained unclear due to the unknown atomic structures of CeNbO4.08 and CeNbO4.33. Here, we report the complex (3 + 1)D incommensurately modulated structure of CeNbO4.08, and the supercell structure of CeNbO4.33 from single nanocrystals by using a three-dimensional electron diffraction technique. Two oxide ion migration events are identified in CeNbO4.08 and CeNbO4.25 by molecular dynamics simulations, which was a synergic-cooperation knock-on mechanism involving continuous breaking and reformation of Nb2O9 units. However, the excess oxygen in CeNbO4.33 hardly migrates because of the high concentration and the ordered distribution of the excess oxide ions. The relationship between the structure and oxide ion migration for the whole series of CeNbO4+δ compounds elucidated here provides a direction for the performance optimization of these compounds.