Zhong Wang,Shuang Yuan,Tuo Zang,Tengxiao Li,Yudi Zhou,Jiaqi Liu,Tie Liu,Kai Wang,Qiang Wang
The noble metal Pt is an ideal catalyst for promoting the hydrogen evolution reaction (HER) during the electrolysis of water. However, Pt is also expensive and suffers from low utilization rates. In this work, a Pt-Ni 2 P/NF nanorod catalyst with a low Pt loading was synthesized under different magnetic fields, and it was found that the application of a magnetic field can increase the rate of the galvanic replacement reaction. When the magnetic field strength increases from 0 to 600 mT, the chemical reaction rate increases gradually, and the utilization rate of Pt increased by 2.3 times under 600 mT. The mechanism of the magnetic field-induced magnetohydrodynamic (MHD) effect on the galvanic replacement reaction was revealed. In a 1 M KOH solution and at a current density of 10 mA cm –2 , the overpotential of Pt-Ni 2 P/NF prepared by applying a 600 mT magnetic field was as low as 15 mV and the Tafel slope was 37 mV dec –1 , compared with values of 82 mV and 70 mV dec –1 for a specimen prepared without a magnetic field. Additionally, at an overpotential of 90 mV, the mass-based Pt activity of the former material was 12 times greater while its turnover frequency was 19 times greater. This work provides theoretical and technical knowledge expected to assist in the controllable preparation of materials in magnetic fields and the efficient utilization of metallic resources.
This study has demonstrated an interesting amplification effect of magnetic field (MF) on the hydroxylamine (HA)-promoted zero valent iron (ZVI)/H 2 O 2 Fenton-like system. Sulfamethoxazole (SMX) could be efficiently degraded at near neutral pH. Conditional parameters affecting the SMX degradation in the ZVI/H 2 O 2 /HA/MF system, e.g. , pH and the dosages of ZVI, HA and H 2 O 2 , were investigated. Unlike the acid-favorable ZVI/H 2 O 2 and ZVI/H 2 O 2 /HA systems, the MF-assisted system exhibited good performances even at pH up to 6.0 and highest degradation rate at pH of 5.0. • OH was still identified as the responsible oxidant. A mechanism involving the MF-enhanced heterogeneous-homogeneous iron cycle was proposed in the near-neutral ZVI/H 2 O 2 /HA system. Without MF, HA-induced reductive dissolution of the surface iron oxides occurred and thus leaded to homogeneous Fenton reactions. After the introduction of MF, the gradient magnetic field formed on the ZVI particles would induce the generation of concentration cells of Fe(II) and local corrosion of iron. Large amounts of aqueous and bounded Fe(II) catalyzed H 2 O 2 to efficiently produce • OH, while HA maintained the surface and bulk cycles of Fe(II)/Fe(III). The result of study is expected to provide a green, energy-free method in improving the effectiveness of ZVI-based Fenton-like technologies at weak-acidic circumstances.
Magnetic field treated perfluorosulfonate ionomer (PFSI) membranes (M-PMs) with improved through-plane proton conductivity are facilely fabricated though solvent casting of PFSI/Fe 3 O 4 nanocomposite dispersion without any third additive under magnetic field followed by discarding the Fe 3 O 4 nanoparticles . In the PFSI/Fe 3 O 4 nanocomposite membrane, Fe 3 O 4 nanoparticles are clearly uniaxially aligned by magnetic field. Subsequently, M-PMs are obtained by removing Fe 3 O 4 from the nanocomposite membranes to eliminate the negative effect of Fe 3 O 4 on proton conducting. The effect of magnetic field treatment on M-PMs' performance is investigated by both in- and through-plane proton conductivity. The results demonstrate that the through-plane proton conductivity of the M-PMs prepared from PFSI/Fe 3 O 4 nanocomposite membrane with optimized Fe 3 O 4 content is enhanced, while the in-plane proton conductivity is reduced compared to the pristine PFSI membrane, which indicate through-plane anisotropic phenomenon of proton conducting in the membranes. Such magnetic field treated PFSI membranes exhibit good appropriateness for using in electrochemical applications, for example fuel cells.
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