No abstract

The applications of the most promising Fe-N-C catalysts are prohibited by their limited intrinsic activities. Manipulating the Fe energy level through anchoring electronwithdrawing ligands is found effective in boosting the catalytic performance.However,such regulation remains elusive as the ligands are only uncontrollably introduced oweingt otheir energetically unstable nature.H erein, we report ar ational manipulation strategy for introducing axial bonded Otothe Fe sites,a ttained through hexa-coordinating Fe with oxygen functional groups in the precursor.M oreover,t he Om odifier is stabilized by forming the Fe À O À Fe bridge bond, with the approximation of two FeN 4 sites.The energy level modulation thus created confers the sites with an intrinsic activity that is over 10 times higher than that of the normal FeN 4 site.O ur finding opens an ovel strategy to manage coordination environments at an atomic level for high activity ORR catalysts.

Lead halide perovskites have shown great potential in photovoltaic and photocatalytic fields. However, the toxicity of lead impedes their wide application. Herein composites of lead-free halide perovskite Cs 2 AgBiBr 6 supported on nitrogen-doped carbon (N-C) materials were synthesized successfully through a facile one-pot method for the first time. Without deposition of noble metals as the cocatalyst, the optimal composite Cs 2 AgBiBr 6 /N-C (Cs 2 AgBiBr 6 /N-C-140) exhibits outstanding photocatalytic performance with a high hydrogen evolution rate of 380 μmol g −1 h −1 under visible light irradiation (λ ≥ 420 nm), which is about 19 times faster than that of pure Cs 2 AgBiBr 6 and 4 times faster than that of physically mixed Cs 2 AgBiBr 6 /N-C-140, respectively. The Cs 2 AgBiBr 6 /N-C-140 composite also displays high stability with no significant decrease after six cycles of repeated hydrogen evolution experiments. The addition of N-C with a high surface area helps to prevent aggregation of Cs 2 AgBiBr 6 NPs and provides more pathways for the migration of photoinduced carriers. The nitrogen dopant can facilitate photoinduced electron transfer from Cs 2 AgBiBr 6 to N-C to result in spatially separated electrons and holes with prolonged electron time and greatly enhance the photocatalytic performance. This study indicates that Cs 2 AgBiBr 6 -based perovskite materials are promising candidates for photocatalytic hydrogen evolution.

Considering the flexibility, adjustable pore structure, and abundant active sites of metal–organic frameworks (MOFs), rational design and fine control of the MOF-based hetero-nanocrystals is a highly important and challenging subject. In this work, self-assembly of a 3D hollow BiOBr@Bi-MOF microsphere was fabricated through precisely controlled dissociation kinetics of the self-sacrificial template (BiOBr) for the first time, where the residual quantity of BiOBr and the formation of Bi-MOF were carefully regulated by changing the reaction time and the capability of coordination. Meanwhile, the hollow microstructure was formed in BiOBr@Bi-MOF through the Oswald ripening mechanism to separate photogenerated electron–hole pairs and increase the adsorption capacity of Bi-MOF for dyes, which significantly enhanced the photocatalytic degradation efficiency of RhB from 56.4% for BiOBr to 99.4% for the optimal BiOBr@Bi-MOF microsphere. This research broadens the selectivity of semiconductor/MOF hetero-nanocrystals with reasonable design and flexible synthesis.