An
electrochemical nitrogen reduction reaction (NRR) under mild
conditions offers a promising alternative to the traditional Haber–Bosch
process in converting abundant nitrogen (N2) to high value-added
ammonia (NH3). In this work, iron phthalocyanine (FePc)
was homogeneously immobilized on pyridine-functionalized carbon nanotubes
to form a well-tuned electrocatalyst with an FeN5 active
center (FePc-Py-CNT). Synchrotron X-ray absorption and Fourier transform
infrared spectroscopy proved the presence of an Fe–N coordination
bond between FePc and surface-bound pyridine. The resulting hybrid
exhibited notably enhanced electrocatalytic NRR performance compared
to FePc immobilized on CNTs based on π–π stacking
interactions (FePc-CNT), resulting in doubled NH3 yield
(21.7 μg mgcat
–1 h–1) and Faradaic efficiency (22.2%). Theoretical calculations revealed
that the axial coordination on FePc resulted in partial electron transfer
from iron to pyridine, which efficiently suppresses the adsorption
of H+ and improves the chemisorption of N2 at
Fe sites. Meanwhile, the interfacial electron transfer was facilitated
by pyridine as an electron transfer relay between FePc and CNTs. This
work provides a unique strategy for the design of highly efficient
NRR electrocatalysts at the molecular level.
Photoelectrochemical reduction of CO 2 is a promising approach for renewable fuel production. We herein report a novel strategy for preparation of hybrid photocathodes by immobilizing molecular cobalt catalysts on TiO 2 -protected n + -p Si electrodes (Si j TiO 2 ) coated with multiwalled carbon nanotubes (CNTs) by ππ stacking. Upon loading a composite of Co II (BrqPy) (BrqPy = 4',4''-bis(4-bromophenyl)-2,2' : 6',2'' : 6'',2'''-quaterpyridine) catalyst and CNT on Si j TiO 2 , a stable 1-Sun photocurrent density of À 1.5 mA cm À 2 was sustained over 2 h in a neutral aqueous solution with unity Faradaic efficiency and selectivity for CO production at a bias of zero overpotential (À 0.11 V vs. RHE), associated with a turnover frequency (TOF CO ) of 2.7 s À 1 . Extending the photoelectrocatalysis to 10 h, a remarkable turnover number (TON CO ) of 57000 was obtained. The high performance shown here is substantially improved from the previously reported photocathodes relying on covalently anchored catalysts.
Developing efficient photocatalysts for water oxidation is among the central challenges of solar energy conversion. Here, we report semiconductor−molecular photocatalysts by integration of heteronuclear bimetallic polyphthalocyanine (PPc) catalysts with particulate bismuth vanadate (BiVO 4 ) as the photosensitizer. Their photocatalytic activity for water oxidation was modulated by tuning the Fe/Co ratio of polyphthalocyanines. At an optimal Fe/Co ratio of 3:1, the resulting Fe 3 CoPPc-BiVO 4 hybrid exhibits an excellent oxygen evolution rate of 4557 μmol g −1 h −1 in the presence of iodate under visible light irradiation, which is nearly two orders of magnitude greater than that of pristine BiVO 4 and superior to those of the corresponding homometallic counterparts. Both experimental and theoretical methods suggest that the presence of a large population of high-valent Fe/Co molecular species due to the favorable interfacial charge transfer and upshift of the d-band centers of metal sites toward Fermi level lead to a lower energy barrier for the O−O bond formation and eventually promote the oxidation of water.
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