RESUMEN
Rational tailoring of the electronic structure at the defined active center of reconstructed metal (oxy)hydroxides (MOOH) during oxygen evolution reaction (OER) remains a challenge. With the guidance of density functional theory (DFT), herein a dual-site regulatory strategy is reported to tailor the d-band center of the Co site in CoOOH via the controlled electronic transfer at the RuâOâCoâOâFe bonding structure. Through the bridged O2- site, electrons are vastly flowed from the t2g-orbital of the Ru site to the low-spin orbital of the Co site in the Ru-O-Co coordination and further transfer from the strong electron-electron repulsion of the Co site to the Fe site by the Co-O-Fe coordination, which balancing the electronic configuration of Co sites to weaken the over-strong adsorption energy barrier of OH* and O*, respectively. Benefiting from the highly active of the Co site, the constructed (Ru2Fe2Co6)OOH provide an extremely low overpotential of 248 mV and a Tafel slope of 32.5 mV dec-1 at 10 mA cm-2 accompanied by long durability in alkaline OER, far superior over the pristine and Co-O-Fe bridged CoOOH catalysts. This work provides guidance for the rational design and in-depth analysis of the optimized role of metal dual-sites.
RESUMEN
The conversion of Li2S4 to Li2S is the most important and slowest rate-limiting step in the complex sulfur reduction reaction (SRR) for Li-S batteries, the adjustment of which can effectively inhibit the notorious "shuttle effect". Herein, a CoSe2-FeSe2 heterostructure embedded in 3D N-doped nanocage as a modified layer on commercial separator is designed (CoSe2-FeSe2@NC//PP). The CoSe2-FeSe2 heterostructure forms a built-in electric field at the two-phase interface, which leads to the optimized adsorption force on polysulfides and the accelerated reaction kinetics for Li2S4-Li2S evolution. Density functional theory (DFT) calculations and experimental results combine to show that the liquid-solid reaction (Li2S4-Li2S2/Li2S) is significantly enhanced in terms of thermodynamics and electrodynamics. Consequently, the batteries assembled with CoSe2-FeSe2@NC//PP delivered an excellent rate capability (606 mAh g-1 under 8.0 C) and a long cycling lifespan (only 0.056% at 1.0 C after 1000 cycles). In addition, the cells can provide high initial capacity of 887 mAh g-1 at sulfur loading of 5.8 mg cm-2 and 0.1 C. This work would provide valuable insights into binary metal selenide heterostructures for liquid-solid conversion in Li-S batteries.