RESUMEN
Composition optimization, structural design, and introduction of external magnetic fields into the catalytic process can remarkably improve the oxygen evolution reaction (OER) performance of a catalyst. NiFe2O4@(Ni, Fe)S/P materials with a heterogeneous core-shell structure were prepared by the sulfide/phosphorus method based on spinel-structured NiFe2O4 nanomicrospheres. After the sulfide/phosphorus treatment, not only the intrinsic activity of the material and the active surface area were increased but also the charge transfer resistance was reduced due to the internal electric field. The overpotential of NiFe2O4@(Ni, Fe)P at 10 mA cm-2 (iR correction), Tafel slope, and charge transfer resistance were 261 mV, 42 mV dec-1, and 3.163 Ω, respectively. With an alternating magnetic field, the overpotential of NiFe2O4@(Ni, Fe)P at 10 mA cm-2 (without iR correction) declined by 45.5% from 323 mV (0 mT) to 176 mV (4.320 mT). Such enhancement of performance is primarily accounted for the enrichment of the reactive ion OH- on the electrode surface induced by the inductive electric potential derived from the Faraday induction effect of the AMF. This condition increased the electrode potential and thus the charge transfer rate on the one hand and weakened the diffusion of the active substance from the electrolyte to the electrode surface on the other hand. The OER process was dominantly controlled by the charge transfer process under low current conditions. A fast charge transfer rate boosted the OER performance of the catalyst. At high currents, diffusion exerted a significant effect on the OER process and low OH- diffusion rates would lead to a decrease in the OER performance of the catalyst.
RESUMEN
Renewable electricity from splitting water to produce hydrogen is a favorable technology to achieve carbon neutrality, but slow anodic oxygen evolution reaction (OER) kinetics limits its large-scale commercialization. Electron spin polarization and increasing the reaction temperature are considered as potential ways to promote alkaline OER. Here, it is reported that in the alkaline OER process under an AC magnetic field, a ferromagnetic ordered electrocatalyst can simultaneously act as a heater and a spin polarizer to achieve significant OER enhancement at a low current density. Moreover, its effect obviously precedes antiferromagnetic, ferrimagnetic, and diamagnetic electrocatalysts. In particular, the noncorrected overpotential of the ferromagnetic electrocatalyst Co at 10 mA cm-2 is reduced by a maximum of 36.6% to 243 mV at 4.320 mT. It is found that the magnetic heating effect is immediate, and more importantly, it is localized and hardly affects the temperature of the entire electrolytic cell. In addition, the spin pinning effect established on the ferromagnetic/paramagnetic interface generated during the reconstruction of the ferromagnetic electrocatalyst expands the ferromagnetic order of the paramagnetic layer. Also, the introduction of an external magnetic field further increases the orderly arrangement of spins, thereby promoting OER. This work provides a reference for the design of high-performance OER electrocatalysts under a magnetic field.
RESUMEN
Adsorption of cationic polyelectrolyte, a homopolymer of maleimide propyl trimethylammonium chloride (MPTMAC), on silica nanoparticles from aqueous solution was studied. The adsorbed amount of MPTMAC and the adsorption layer thickness from solutions of different pH, polyelectrolyte concentration, salt type, and salt concentration were measured. The adsorbed amount exhibited a maximum as a function of the electrolyte concentration. The onset of the decline in the adsorbed amount depended on the type of counterions. The thickness of the adsorption layer increased gradually with increased of electrolyte concentration and leveled off at high electrolyte concentration. The enhanced adsorption in the presence of Na2SO4 can be explained by the bivalent SO4(2-) causing a better shielding effect. With increasing pH the adsorbed amount of MPTMAC increased, whereas the thickness of an adsorbed layer of MPTMAC decreased. At low polyelectrolyte concentrations unstable silica suspensions were observed from a stability test. At high polyelectrolyte concentrations the higher particle coverage caused electrosteric stabilization of the dispersion. However, further increase in MPTMAC concentration after saturated adsorption would flocculate the dispersed system. At low pH, MPTMAC tending to create a loops or tails conformation stabilized the suspension.
RESUMEN
In this paper, we synthesize a new ligand of 1-ethyl-2-(naphthalen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (Phen-Np-Et) and its corresponding Cu(I) complex of [Cu(Phen-Np-Et)(POP)]BF(4), where POP is bis(2-(diphenylphosphanyl)phenyl) ether. The single-crystal structure, electronic nature and photophysical property of [Cu(Phen-Np-Et)(POP)]BF(4) are discussed in detail. It is found that the yellow emission from [Cu(Phen-Np-Et)(POP)]BF(4) owns a long excited state lifetime of 287 µs under pure N(2) atmosphere. Theoretical calculation on [Cu(Phen-Np-Et)(POP)](+) suggests that the emission comes from a triplet metal-to-ligand-charge-transfer excited state. Then, [Cu(Phen-Np-Et)(POP)]BF(4) are doped into two matrixes of polystyrene and MCM-41 to investigate the oxygen-sensing performance. Finally, sensitivity maxima of 9.6 and 3.6 are achieved by the composite nanofibers of [Cu(Phen-Np-Et)(POP)]BF(4)/polystyrene and the [Cu(Phen-Np-Et)(POP)]BF(4)/MCM-41, respectively. Both samples are highly sensitive toward molecular oxygen, owing to the large surface-area-to-volume ratios of nanofibrous membranes and MCM-41 matrix.