Search

In situ growth of intertwined trinuclear copper complexes (nCu3) on a cellulose-derived carbon support (CMC) produced a high-performance electrocatalyst (CMC–nCu3) for the oxygen reduction reaction (ORR), which demonstrated superior performance in zinc–air batteries compared to a commercial Pt/C catalyst. This work highlights the importance of copper-based molecular catalysts with rich and intertwined tricopper structures for boosting both ORR activity and stability. [ABSTRACT FROM AUTHOR]

Bioinspired by the active sites of multicopper oxidases (MCOs), bi/multinuclear copper complexes have attracted great attention in promoting catalytic activity for the oxygen reduction reaction (ORR). Herein, we report the preparation of a Cu–N–C electrocatalyst Cu-BPOZ@CNB-400 for efficient ORR, which was obtained by low temperature pyrolysis of a dinuclear 2,5-bis(2-pyridyl)-1,3,4-oxadiazole (BPOZ) copper complex loaded on a N-doped carbon support at 400 °C. Cu-BPOZ@CNB-400 exhibited a half-wave potential (E1/2) of 0.86 V vs. RHE for the ORR in 0.1 M KOH solution, which was significantly higher than that of the Cu-BPOZ@CNB-800 (E1/2 = 0.83 V) catalyst treated under high temperature (at 800 °C) and the control catalyst Cu-Phen@CNB-400 (E1/2 = 0.82 V) derived from low-temperature-treatment (at 400 °C) of a mononuclear phenanthroline-coordinated-Cu complex loaded on a N-doped carbon support. When Cu-BPOZ@CNB-400 was applied as the cathode catalyst in zinc–air batteries a maximum power density (Pmax) of 127 mW cm−2 could be achieved, demonstrating comparable catalyst performance to the commercial 20 wt% Pt/C (Pmax = 122 mW cm−2) and the control Cu-Phen@CNB-400 catalyst (Pmax = 105 mW cm−2) under similar experimental conditions. Low-temperature pyrolysis of dinuclear copper complexes on a carbon support improved the charge transfer efficiency, inhibited metal aggregation, and could produce highly dispersed Cu–N–C catalysts with dinuclear copper sites for promoting the 4e−-reduction selectivity of the ORR. It thus provides a cost-effective approach for the controllable fabrication of efficient ORR catalysts to be applied for energy conversion devices. [ABSTRACT FROM AUTHOR]

Developing efficient non‐precious metal electrocatalysts to replace Pt‐based noble metal catalysts for oxygen reduction reaction (ORR) in energy conversion devices is highly desirable. Atomically dispersed Fe−N−C catalysts are the most promising alternatives of Pt for ORR; however, enhancing their intrinsic activity via active site modulation is still a challenge. Using an iron porphyrin‐functionalized MOFs as the precursor, we prepared a defects‐rich Fe−N−C catalyst and modulated its intrinsic activity by creating defects near the Fe−Nx sites through decarboxylation reaction. Due to the synergistic effect of the improved porous structure and created defects, the prepared Defects‐FeNC exhibited excellent performance for ORR with half‐wave potential of 0.895 V vs. RHE in alkaline media. The Defects‐FeNC loaded Zn‐Air battery delivered much higher open circuit potential (OCP=1.463 V) and maximum power density (Pmax=151 mW cm−2) than the commercial 20 wt.% Pt/C (OCP=1.441 V; Pmax=119 mW cm−2) under similar experimental conditions. Defects in the catalyst could modulate the electronic structure of the Fe−Nx−C center that further promoted the catalyst catalytic activity for ORR. This work provides a facile active‐sites‐engineering approach for boosting the Fe−N−C catalyst ORR performance, which shows promising implications in energy conversion devices. [ABSTRACT FROM AUTHOR]

Zn‐air battery is a promising next‐generation energy storage device. Its performance, however, is limited by a high overpotential resulted from the slow kinetics of the cathodic oxygen reduction reaction (ORR). This study reports a simple strategy for preparation of a fluorine‐doped Co−N−C composite as highly efficient electrocatalyst for ORR. The C@PVI‐(TPFC)Co‐800 catalyst was prepared by pyrolysis of F‐containing Co‐corrole that was assembled on PVI‐functionalized carbon black through the axial imidazole coordination (PVI=polyvinylimidazole, TPFC=5,10,15‐triperfluorophenyl‐21H, 22H‐corrole). The C@PVI‐(TPFC)Co‐800 catalyst exhibited much more positive ORR half‐wave potential (E1/2=0.88 V vs. RHE) than its counterpart C@PVI‐(TPC)Co‐800 (E1/2=0.82 V, TPC=5,10,15‐triphenyl‐21H, 22H‐corrole) without F‐doping in 0.1 M KOH electrolyte. C@PVI‐(TPFC)Co‐800 also achieved a greater kinetic current density and enhanced durability in alkaline media. In addition, a Zn‐air battery with C@PVI‐(TPFC)Co‐800 loaded at the cathode delivered much higher peak power density (Pmax=141 mW/cm2) and open‐circuit voltage (OCV=1.45 V) over the C@PVI‐(TPC)Co‐800 counterpart (Pmax=110 mW/cm2, OCV=1.39 V) and the commercial 20 % Pt/C (Pmax=119 mW/cm2, OCV=1.42 V) as well. The promoted catalyst performance for ORR was attributed to the increased specific surface area, more defects generated, and reduced electron density distribution around the Co metal center after F‐doping. [ABSTRACT FROM AUTHOR]

A P-doped PtNi alloy loaded on N,C-doped TiO2 nanosheets (P–PtNi@N,C–TiO2) exhibited excellent activity and durability for the oxygen reduction reaction (ORR) in 0.1 M HClO4 solution with mass (4×) and specific (6×) activity several times higher than those of commercial 20 wt% Pt/C, respectively. The P dopant mitigated the dissolution of Ni and strong interactions between the catalyst and the N,C–TiO2 support inhibited catalyst migration. This provides a new approach for the design of high-performance non-carbon-supported low-Pt catalysts to be used in harsh acidic environments. [ABSTRACT FROM AUTHOR]

Fine tuning of the metal site coordination environment of a single-atom catalyst (SAC) to boost its catalytic activity for oxygen reduction reaction (ORR) is of significance but challenging. Herein, we report a new SAC bearing Fe-N 3 C-N sites with asymmetric in-plane coordinated Fe-N 3 C and axial coordinated N atom for ORR, which was obtained by pyrolysis of an iron isoporphyrin on polyvinylimidazole (PVI) coated carbon black. The C@PVI-(NCTPP)Fe-800 catalyst exhibited significantly improved ORR activity ( E 1/2 = 0.89 V vs RHE) than the counterpart SAC with Fe-N 4 -N sites in 0.1 M KOH. Significantly, the Zn-air batteries equipped with the C@PVI-(NCTPP)Fe-800 catalyst demonstrated an open-circuit voltage (OCV) of 1.45 V and a peak power density ( P max ) of 130 mW/cm 2 , outperforming the commercial Pt/C catalyst (OCV = 1.42 V; P max = 119 mW/cm 2 ). The density functional theory (DFT) calculations revealed that the d-band center of the asymmetric Fe-N 3 C-N structure shifted upward, which enhances its electron-donating ability, favors O 2 adsorption, and supports O-O bond activation, thus leading to significantly promoted catalytic activity. This research presents an intriguing strategy for the designing of the active site architecture in metal SACs with a structure-function controlled approach, significantly enhancing their catalytic efficiency for the ORR and offering promising prospects in energy-conversion technologies.

Bioinspired by the active sites of multicopper oxidases (MCOs), bi/multinuclear copper complexes have attracted great attention in promoting catalytic activity for the oxygen reduction reaction (ORR). Herein, we report the preparation of a Cu-N-C electrocatalyst Cu-BPOZ@CNB-400 for efficient ORR, which was obtained by low temperature pyrolysis of a dinuclear 2,5-bis(2-pyridyl)-1,3,4-oxadiazole (BPOZ) copper complex loaded on a N-doped carbon support at 400 °C. Cu-BPOZ@CNB-400 exhibited a half-wave potential ( E 1/2 ) of 0.86 V vs. RHE for the ORR in 0.1 M KOH solution, which was significantly higher than that of the Cu-BPOZ@CNB-800 ( E 1/2 = 0.83 V) catalyst treated under high temperature (at 800 °C) and the control catalyst Cu-Phen@CNB-400 ( E 1/2 = 0.82 V) derived from low-temperature-treatment (at 400 °C) of a mononuclear phenanthroline-coordinated-Cu complex loaded on a N-doped carbon support. When Cu-BPOZ@CNB-400 was applied as the cathode catalyst in zinc-air batteries a maximum power density ( P max ) of 127 mW cm -2 could be achieved, demonstrating comparable catalyst performance to the commercial 20 wt% Pt/C ( P max = 122 mW cm -2 ) and the control Cu-Phen@CNB-400 catalyst ( P max = 105 mW cm -2 ) under similar experimental conditions. Low-temperature pyrolysis of dinuclear copper complexes on a carbon support improved the charge transfer efficiency, inhibited metal aggregation, and could produce highly dispersed Cu-N-C catalysts with dinuclear copper sites for promoting the 4e - -reduction selectivity of the ORR. It thus provides a cost-effective approach for the controllable fabrication of efficient ORR catalysts to be applied for energy conversion devices.

Developing high performance noble-metal-free electrocatalysts as an alternative to Pt-based catalysts for the oxygen reduction reaction (ORR) in energy conversion devices is highly desirable. We report herein the preparation of a coordination-polymer (CP)-derived Fe/CP/C composite as an electrocatalyst for the ORR with excellent activity and stability both in solution and in Zn-air batteries. The Fe/CP/C catalyst was obtained from the pyrolysis of an iron porphyrin Fe(TPP)Cl (5,10,15,20-tetraphenyl-21 H ,23 H -porphyrin iron(III) chloride) grafted Zn-coordination polymer with dangling functional groups 4,4'-oxybisbenzoic acid and 4,4'-bipyridine ligands. The Fe/CP/C catalyst showed much higher ORR activity with a half-wave potential ( E 1/2 ) of 0.90 V ( vs. RHE) than the Fe/C catalyst ( E 1/2 = 0.85 V) derived from the carbon-black-supported Fe porphyrins in 0.1 M KOH solution. When Fe/CP/C was used as the cathode electrocatalyst in Zn-air batteries (ZABs), the ZABs achieved a significantly higher open circuit voltage (OCV = 1.43 V) and maximum power density ( P max = 142.8 mW cm -2 ) compared with Fe/C (OCV = 1.38 V, P max = 104.5 mW cm -2 ) and commercial 20 wt% Pt/C (OCV = 1.41 V, P max = 117.6 mW cm -2 ). Using dangling functional groups in CP to increase the loading efficiency of iron porphyrins offered a facile method to prepare high-performance noble-metal-free electrocatalysts for the ORR, which may provide promising applications to energy conversion devices.

Promoting the catalyst performance for oxygen reduction reaction (ORR) in energy conversion devices through controlled manipulation of the structure of catalytic active sites has been a major challenge. In this work, we prepared Fe-N-C single-atom catalysts (SACs) with Fe-N 5 active sites and found that the catalytic activity of the catalyst with shrinkable Fe-N 5 -C 11 sites for ORR was significantly improved compared with the catalyst bearing normal Fe-N 5 -C 12 sites. The catalyst C@PVI-(TPC)Fe-800, prepared by pyrolyzing an axial-imidazole-coordinated iron corrole precursor, exhibited positive shifted half-wave potential ( E 1/2 = 0.89 V vs RHE) and higher peak power density ( P max = 129 mW/cm 2 ) than the iron porphyrin-derived counterpart C@PVI-(TPP)Fe-800 ( E 1/2 = 0.81 V, P max = 110 mW/cm 2 ) in 0.1 M KOH electrolyte and Zn-air batteries, respectively. X-ray absorption spectroscopy (XAS) analysis of C@PVI-(TPC)Fe-800 revealed a contracted Fe-N 5 -C 11 structure with iron in a higher oxidation state than the porphyrin-derived Fe-N 5 -C 12 counterpart. Density functional theory (DFT) calculations demonstrated that C@PVI-(TPC)Fe-800 possesses a higher HOMO energy level than C@PVI-(TPP)Fe-800, which can increase its electron-donating ability and thus help achieve enhanced O 2 adsorption as well as O-O bond activation. This work provides a new approach to tune the active site structure of SACs with unique contracted Fe-N 5 -C 11 sites that remarkably promote the catalyst performance, suggesting significant implications for catalyst design in energy conversion devices.

A P-doped PtNi alloy loaded on N,C-doped TiO 2 nanosheets (P-PtNi@N,C-TiO 2 ) exhibited excellent activity and durability for the oxygen reduction reaction (ORR) in 0.1 M HClO 4 solution with mass (4×) and specific (6×) activity several times higher than those of commercial 20 wt% Pt/C, respectively. The P dopant mitigated the dissolution of Ni and strong interactions between the catalyst and the N,C-TiO 2 support inhibited catalyst migration. This provides a new approach for the design of high-performance non-carbon-supported low-Pt catalysts to be used in harsh acidic environments.

The oxygen reduction reaction (ORR) is essential in many life processes and energy conversion systems. It is desirable to design transition metal molecular catalysts inspired by enzymatic oxygen activation/reduction processes as an alternative to noble-metal-Pt-based ORR electrocatalysts, especially in view point of fuel cell commercialization. We have fabricated bio-inspired molecular catalysts electrografted onto multiwalled carbon nanotubes (MWCNTs) in which 5,10,15,20-tetra(pentafluorophenyl) iron porphyrin (iron porphyrin FeF 20 TPP) is coordinated with covalently electrografted axial ligands varying from thiophene to imidazole on the MWCNTs' surface. The catalysts' electrocatalytic activity varied with the axial coordination environment (i. e., S-thiophene, N-imidazole, and O-carboxylate); the imidazole-coordinated catalyst MWCNTs-Im-FeF 20 TPP exhibited the highest ORR activity among the prepared catalysts. When MWCNT-Im-FeF 20 TPP was loaded onto the cathode of a zinc-air battery, an open-cell voltage (OCV) of 1.35 V and a maximum power density (P max ) of 110 mW cm -2 were achieved; this was higher than those of MWCNTs-Thi-FeF 20 TPP (OCV=1.30 V, P max =100 mW cm -2 ) and MWCNTs-Ox-FeF 20 TPP (OCV=1.28 V, P max =86 mW cm -2 ) and comparable with a commercial Pt/C catalyst (OCV=1.45 V, P max =120 mW cm -2 ) under similar experimental conditions. This study provides a time-saving method to prepare covalently immobilized molecular electrocatalysts on carbon-based materials with structure-performance correlation that is also applicable to the design of other electrografted catalysts for energy conversion., (© 2021 Wiley-VCH GmbH.)

Schisandrin, derived from the Chinese medicinal herb Schisandra chinensis, has been found to confer protective effects on circulation systems. But the underlying molecular mechanisms remain unclear. The aim of this study was to investigate the effects of a high level of glucose on RhoA and eNOS activity in human umbilical vein endothelial cells(HUVECs) and how Schisandrin plays a role in mediating these effects. To find the optimal treatment time, HUVECs were cultured at a high glucose concentration (30 mM) for different lengths of time (0, 12, 24, and 48 h). Subsequently, the cells were randomized into five groups: a normal group, a high glucose group, and three high glucose groups that were given different doses (5, 10, and 20 μM) of Schisandrin. The cells were pretreated with Schisandrin for 24 h before stimulation with high glucose. The morphology of HUVECs in the various groups was assessed under a light microscope. Immunocytochemical staining was used to detect the level of p-MYPT1 expression. The levels of RhoA activity were determined using the RhoA Activation Assay Biochem Kit. The levels of eNOS activity were examined using a nitrate reduction test. The results showed that in the high glucose group, the activity of RhoA was increased and the activity of eNOS was reduced, thus decreasing the secretion of NO. However, after pretreatment with Schisandrin (10, 20 μM), the activity of RhoA was inhibited and the activity of eNOS increased, which led to an increase in NO production compared with the high glucose group. There was no evident difference between the 5 μM Schisandrin group and the high glucose group. Taken together, these findings indicate that Schisandrin can improve the function of endothelial cells by lowering the activity of RhoA/Rho kinase and raising both the activity of eNOS and the production of NO., (Copyright © 2018 Elsevier GmbH. All rights reserved.)