well-tuned electronic configuration. [4,5] Especially, with an edge-sharing octahedral MO 6 layer-stacking crystal structure served as highly active sites, NiFe-based layered double hydroxides (NiFe LDHs) exhibited highly remarkable intrinsic electrochemical activity. [6,7] Several studies have reported that NiFe LDH is actually a precatalyst, and it heavily undergoes a self-reconstruction process in basic solution, generating Ni oxyhydroxide (NiOOH) as the active species for OER. [8,9] To begin with, Alexis et al. characterized the vibration mode of NiOOH by in situ Raman spectra, when Ni-Fe films worked as anodes in basic media during the OER. [10] Then, some research revealed that NiOOH species is generally recognized as the positive reaction species and can provide abundant intrinsic catalytic sites for OER. [11][12][13] Not limited to OER, NiOOH can also efficiently catalyze the anodic degradation of urea that featured with the more complex six-electron redox process. [14,15] However, owing to the instability of the high valence state of Ni (III) which can easily transform into Ni (II), the direct synthesis and application of NiOOH have not been realized, unless a high anodic polarization is applied. [16,17] Therefore, it is crucial to explore synthesis methods to stabilize NiOOH catalyst.Among the multiple regulation methods, surface structure reconstruction with the aid of a new phase is widely accepted as a controllable approach for synthesizing novel composites with NiOOH is considered as the most active intermediate during electrochemical oxidation reaction, however, it is hard to directly synthesize due to high oxidation energy. Herein, theoretical calculations predict that α-FeOOH enables a decline in formation energy and an improvement in stabilization of NiOOH in NiFe-based layered double hydroxide (LDH). Inspiringly, a composite composed of α-FeOOH and LDH is well-designed and successfully fabricated in hydrothermal treatment by adding extra Fe 3+ resource, and stable NiOOH is obtained by the following electro-oxidation method. Benefiting from strong electron-capturing capability of α-FeOOH, it efficiently promotes charge redistribution around the Ni/Fe sites and activates Ni atoms of LDH, verified by X-ray photoelectron spectra (XPS) and X-ray absorption spectra (XAS). The d-band center is optimized that balances the absorption and desorption energy, and thus Gibbs free energy barrier is lowered dramatically toward oxygen evolution reaction (OER) and urea oxidation reaction (UOR), and finally showing an outstanding overpotential of 195 mV and a potential of 1.35 V at 10 mA cm −2 , respectively. This study provides a novel strategy to construct highly efficient catalysts via the introduction of a new phase for complex multiple-electron reactions.
The electronic structure of composites plays a critical role in photocatalytic conversion, whereas it is challenging to modulate the orbital for an efficient catalyst. Herein, we regulated the t 2g orbital occupancy state of Ti to realize efficient CO 2 conversion by adjusting the amount of photo-deposited Cu in the Cu/ TiO 2 composite. For the optimal sample, considerable electrons transfer from the Cu d orbital to the Ti t 2g orbital, as proven by X-ray absorption spectroscopy. The Raman spectra results also corroborate the electron enrichment on the Ti t 2g orbital. Further theoretical calculations suggested that the orbital energy of the Ti 3d orbital in TiO 2 is declined, contributing to accepting Cu 3d electrons. As a result, the Cu/TiO 2 composite exhibited an extremely high selectivity of 95.9 % for CO, and the productivity was 15.27 μmol g À 1 h À 1 , which is almost 6 times that of the original TiO 2 . Our work provides a strategy for designing efficient photocatalysis as a function of orbital regulation.
Anionic redox chemistry is becoming increasingly important in explaining the intristic catalytic behavior in transition-metal oxides and improving catalytic activity. However, it is a great challenge to activate lattice oxygen in noble-metal-free perovskites for obtaining active peroxide species. Here, we take LaSrCoO as a model catalyst and develop an anionic redox activity regulation method to activate lattice oxygen by tuning charge transfer between Co and O. Advanced XAS and XPS demonstrate that our method can effectively decrease electron density of surface oxygen sites (O) to form more reactive oxygen species (O), which reduces the activation energy barriers of molecular O and leads to a very high CO catalytic activity. The revealing of the activation mechanism for surface oxygen sites in perovskites in this work opens up a new avenue to design efficient solid catalysts. Furthermore, we also establish a correlation between anionic redox chemistry and CO catalytic activity.
A simple treatment of La0.5Sr0.5MnO3 with diluted HNO3 creates more B-sites (rich) on the terminated perovskite surface and improves its catalytic activity toward CO oxidation, and the perovskite catalyst possesses a higher ratio of Mn(4+)/Mn(3+) and thus enhances the O2 adsorption capability, favourable for CO oxidation and catalytic activity.
Atemperature-controlled cation-exchange approach is introduced to achieve aunique dual-exsolution in perovskite La 0.8 Fe 0.9 Co 0.1 O 3Àd where both CoFea lloy and Co metal are simultaneously exsolved from the parent perovskite,f orming an alloya nd metal co-decorated perovskite oxide.M ossbauer spectra showt hat cation exchange of Fe atoms in CoFea lloy and Co cations in the perovskite is the key to the co-existence of Co metal and CoFealloy. The obtained composite exhibits an enhanced catalytic activity as Li-O 2 battery cathode catalysts with as pecific discharge capacity of 6549.7 mAh g À1 and ac ycling performance of 215 cycles without noticeable degradation. Calculations showt hat the combination of decorated CoFea lloya nd Co metal synergistically modulated the discharge reaction pathway that improves the performance of Li-O 2 battery.
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