Nanoporous electrodes of phase-dealloyed Fe83.3-xCoxSi4B8P4Cu0.7 (x = 4, 10 and 20 at.%) precursors with superior Redox performances and high stabilities

Abstract

Co substitutions for Fe83.3Si4B8P4Cu0.7 precursors are effective to stabilize the nanoporous structures during dealloying in H2SO4 solutions and improve Redox performances of nanoporous electrodes in alkaline conditions. Heterogeneous nanocrystalline structures of Co-substituted Fe83.3-xCoxSi4B8P4Cu0.7 (x = 0, 4, 10 and 20 at.%) alloys consist of two phases: α-Fe(Co) phases and continuously distributed residual amorphous phases. The nanopores on as-dealloyed Fe-Co-Si-B-P-Cu alloys are smaller in size with higher Co concentrations. This is ascribed to the finer α-Fe(Co) phases distributed in the precursor alloys after nanocrystallization. Nanoporous architectures after dealloying inherit the microstructural characteristics of Fe-Co-Si-B-P-Cu precursor alloys. The short-term and long-term CV curves of nanoporous Redox electrodes in 0.5 M KOH solution demonstrate that Redox reactions have been enhanced by partial substitution of Fe by Co and the best Redox performance can be obtained on as-dealloyed Fe79.3Co4Si4B8P4Cu0.7 alloys because of the highest Redox peak current density of 90 mA cm−2 after 150 CV cycles. However, the stabilities of nanoporous Fe79.3Co4Si4B8P4Cu0.7 electrodes have a predictable decline due to the overgrowth of Fe3O4 octahedra and destruction of the ligaments during long-term Redox cycling. On the other hand, the better Redox stabilities has achieved on as-dealloyed Fe63.3Co20Si4B8P4Cu0.7 alloys with stable oxidation peak current densities of 45–47 mA cm−2 from 950 to 3000 CV cycles, about 2.3 times the nanoporous Co-free Fe83.3Si4B8P4Cu0.7 electrodes. The stabilities are considered to result from the relatively small Fe3O4 octahedra, the stabilization of the amorphous Co3O4 outmost layers and the transformation of amorphous and crystalline Co3O4 phases during long-term Redox cycling. The Co substitution of Fe83.3Si4B8P4Cu0.7 precursor alloys can achieve the high Redox performances and good stabilities of nanoporous electrodes.