An investigation of the structural and electronic origins of enhanced chemical looping air separation performance of B-site substituted SrFe1-xCoxO3-δ perovskites.

Chemical looping air separation (CLAS) is a promising process intensification technology for extracting oxygen from air for oxygen enrichment in process streams. Co-doped strontium ferrites (SrFe1-xCoxO3-δ) have been found to have outstanding activities for CLAS processes. In this study, we explore the underlying factors driving the enhancement in oxygen uptake and release performance of perovskite structured SrFe1-xCoxO3-δ oxygen carriers for CLAS. Phase-pure perovskites, with B site substituted by up to 75 mol% Co, were prepared by a sol-gel method and systematically investigated through a wide range of well controlled experimental and computational approaches. While all SrFe1-xCoxO3-δ oxygen carriers showed excellent cyclic stability and structural reversibility over CLAS cycles, increased B site occupancy by Co resulted in monotonic decrease in onset temperature for oxygen release and increase in oxygen carrying capacity. These experimental trends can be fundamentally explained by an increase in the structural tolerance factor, an elevation in transition metal d-band, as well as an increased degree of hybridization between the metal d-band and the O p band. Therefore, these ab initio structural and electronic descriptors are useful design rationales for the hypothesis-driven synthesis of high-performing oxygen carriers for CLAS.

Two Anthracene-Based Ir(III) Complexes [Ir(pbt)2(aip)]Cl and [Ir(pbt)2(aipm)]Cl: Relationship between Substituent Group and Photo-oxidation Activity as Well as Photo-oxidation-Induced Luminescence.

Two anthracene-based complexes [Ir(pbt)2(aip)]Cl (1) and [Ir(pbt)2(aipm)]Cl (2) have been synthesized based on the ligands aip = 2-(9-anthryl)-1H-imidazo[4,5-f][1,10]phenanthroline, aipm = 2-(9-anthryl)-1-methyl-imidazo[4,5-f][1,10]phenanthroline, and pbtH = 2-phenylbenzothiazole in order to explore both the influence of the substituent group R1 (R1 = H in 1 and CH3 in 2) on photo-oxidation activity and photo-oxidation-induced luminescence. Both 1H NMR spectra and ES mass spectra indicate that the anthracene moiety in complex 1 can be oxidized at room temperature upon irradiation with 365 nm light. Thus, this complex shows photo-oxidation-induced turn-on yellow luminescence. Compared to 1, complex 2 incorporates an R1 = CH3 group, resulting in very weak photo-oxidation activity. On the basis of experimental results and quantum chemical calculation, we report the differences between 1 and 2 in both photo-oxidation behavior and the related luminescence modulation and discuss the relationship between photo-oxidation activity and substituent group R1 in these complexes.

Active and highly durable supported catalysts for proton exchange membrane electrolysers.

The design and development of supported catalysts for the oxygen evolution reaction (OER) is a promising pathway to reducing iridium loading in proton exchange membrane water electrolysers. However, supported catalysts often suffer from poor activity and durability, particularly when deployed in membrane electrode assemblies. In this work, we deploy iridium coated hollow titanium dioxide particles as OER catalysts to achieve higher Ir mass activities than the leading commercial catalysts. Critically, we demonstrate state-of-the-art durabilities for supported iridium catalysts when compared against the previously reported values for analogous device architectures, operating conditions and accelerated stress test profiles. Through extensive materials characterisations alongside rotating disk electrode measurements, we investigate the role of conductivity, morphology, oxidation state and crystallinity on the OER electrochemical performance. Our work highlights a new supported catalyst design that unlocks high-performance OER activity and durability in commercially relevant testing configurations.

Defect Engineering of Low-Coordinated Metal-Organic Frameworks (MOFs) for Improved CO2 Access and Capture.

While metal-organic frameworks (MOFs) are promising gas adsorbents, their tortuous microporous structures cause additional resistance for gas diffusion, thus hindering the accessibility of interior active sites. Here, we present a practical strategy to incorporate missing cluster defects into a representative low-coordinated MOFs structure, Mg-MOF-74, while maintaining the stability of a defect-rich structure. In this proposed method, graphene oxide (GO) is employed as modulator, and crystallization time is varied to promote defect formation by altering the nucleation and crystal growth processes. The best performing GO-modified Mg-MOF-74 sample (MOF@GO 40 h) achieved 18% and 15% improvement in surface area and total pore volume, respectively, over pristine Mg-MOF-74. The reduced diffusion resistance to gas flow translates to increased accessibility for gas molecules to active Mg adsorption sites inside the MOFs, leading to enhanced CO2 capture performance; the CO2 uptake quantity of MOF@GO 40 h arrives at 6.06 mmol/g at 0.1 bar and at 9.17 mmol/g at 1 bar and 25 °C, 19.29% and 16.37% higher, respectively, than that of the pristine Mg-MOF-74, with a CO2/N2 selectivity around 17.36% greater than that of pristine Mg-MOF-74. Our study demonstrates a facile approach for incorporating defects into MOFs systems with low coordination environments, thus expanding the library of defect-rich MOFs beyond the current highly coordinated MOF systems.

Cyclometalated Ir(iii) complexes based on 2-(2,4-difluorophenyl)-pyridine and 2,2'-(2-phenyl-1H-imidazole-4,5-diyl)dipyridine: acid/base-induced structural transformation and luminescence switching, and photocatalytic activity for hydrogen evolution.

Based on ligands dfppyH and pidpyH, cyclometalated Ir(iii) complexes [Ir(dfppy)2(pidpyH)](PF6) (1·PF6) and [Ir(dfppy)2(pidpy)] (2) have been synthesized. The crystal structures indicate that each {Ir(dfppy)2}+ unit is coordinated by a neutral ligand pidpyH in 1·PF6, while by a pidpy- anion in 2. The packing structure of 1·PF6 only exhibits electrostatic interactions and van der Waals interactions among [Ir(dfppy)2(pidpyH)]+ cations and PF6- ions. In contrast, the neighboring molecules in 2 are linked into a supramolecular chain structure through aromatic stacking interactions between two dfppy- ligands. In solution, 1·PF6 and 2 show acid/base-induced structural transformation due to the protonation/deprotonation of their pyridyl groups and/or imidazole units, which can be confirmed by their 1H NMR spectra. At room temperature, compounds 1·PF6, 2 and pidpyH in CH2Cl2 reveal TFA-induced luminescence switching behaviors, from a non-luminescence state to a luminescence state with an emission at 582 nm for both 1·PF6 and 2, and emission switching from 392 nm to 502 nm for pidpyH. These switching behaviors are associated with the protonation of pyridyl groups and/or imidazole units in 1·PF6, 2 and pidpyH. Moreover, compounds 1·PF6 and 2 were used as photosensitizers (PS) for reduction of water to hydrogen under the same experimental conditions. It was found that the amount of evolved hydrogen and the PS turnover number are 512 µmol and 102 for 1·PF6, and 131 µmol and 26 for 2, respectively. Thus, compound 1·PF6 has better photocatalytic activity than 2. In this paper, we discuss the modulation of luminescence and photocatalytic activities of 1·PF6 and 2 by varying the coordination mode and/or protonation extent of pidpyH/pidpy- ligands.