RESUMEN
Lithium-oxygen batteries (LOBs) with ultra-high theoretical energy density (≈3500 Wh kg-1 ) are considered as the most promising energy storage systems. However, the sluggish kinetics during the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) can induce large voltage hysteresis, inferior roundtrip efficiency and unsatisfactory cyclic stability. Herein, hydrangea-like NiO@Ni2 P heterogeneous microspheres are elaborately designed as high-efficiency oxygen electrodes for LOBs. Benefitting from the interfacial electron redistribution on NiO@Ni2 P heterostructure, the electronic structure can be modulated to ameliorate the chemisorption of the intermediates, which is confirmed by density functional theory (DFT) calculations and experimental characterizations. In addition, the interpenetration of the PO bond at the NiO@Ni2 P heterointerface leads to the internal doping effect, thereby boosting electron transfer to further improve ORR and OER activities. As a result, the NiO@Ni2 P electrode shows a low overpotential of only 0.69 V, high specific capacity of 18254.1 mA h g-1 and superior long-term cycling stability of over 1400 h. The exploration of novel bifunctional electrocatalyst in this work provides a new solution for the practical application of LOBs.
RESUMEN
Electronic structural engineering plays a key role in the design of high-efficiency catalysts. Here, to achieve optimal electronic states, introduction of exotic Fe dopant and Co vacancy into CoSe2 nanosheet (denoted as Fe-CoSe2-VCo) is presented. The obtained Fe-CoSe2-VCo demonstrates excellent catalytic activity as compared to CoSe2. Experimental results and density functional theory (DFT) calculations confirm that Fe dopant and Co defects cause significant electron delocalization, which reduces the adsorption energy of LiO2 intermediate on the catalyst surface, thereby obviously improving the electrocatalytic activity of Fe-CoSe2-VCo towards oxygen redox reactions. Moreover, the synergistic effect between Co vacancy and Fe dopant is able to optimize the microscopic electronic structure of Co ion, further reducing the energy barrier of oxygen electrode reactions on Fe-CoSe2-VCo. And the lithium-oxygen batteries (LOBs) based on Fe-CoSe2-VCo electrodes demonstrate a high Coulombic efficiency (CE) of about 72.66%, a large discharge capacity of about 13723 mA h g-1, and an excellent cycling life of about 1338 h. In general, the electronic structure modulation strategy with the reasonable introduction of vacancy and dopant is expected to inspire the design of highly efficient catalysts for various electrochemical systems.
RESUMEN
The rational design of the surface structure and morphology characteristics of the catalyst at atomic level are the key to improve the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in lithium-oxygen (Li-O2) battery. Here a series of cobalt phosphide (CoP) electrocatalysts with a variety of index facets are successfully prepared including concave polyhedrons CoP exposing with (211) crystal planes (CoP CPHs) spherical nanoparticles CoP exposed with (011) crystal planes and polyhedron particles CoP exposing with (011) and (111) crystal planes. The results show that CoP CPHs based Li-O2 battery presents a large discharge capacity of 33743 mA h g-1 at current density of 50 mA g-1 and a remarkable long cycle life of up to 950 h. The experimental results demonstrates that the CoP CPHs electrode exposing with high-index (211) facets based Li-O2 battery exhibits an extremely low overpotential (0.67 V) ultrahigh specific capacity (33743 mAh g-1) and remarkable long-term stability of up to 950 h. Most importantly density functional theory (DFT) calculations demonstrate the excellent electrocatalytic activity of high-index (211) facets as compared to the low-index (011) and (111) planes are because of the existence of large density of atomic steps edge ledge sites and kinks which supply a wide space for breaking chemical bonds and increasing the reaction activity for oxygen electrode.
RESUMEN
Exploring oxygen electrodes with superior bifunctional catalytic activity and suitable architecture is an effective strategy to improve the performance of lithium-oxygen (Li-O2) batteries. Herein, the internal electronic structure of Ni2P is regulated by heteroatom Co doping to improve its catalytic activity for oxygen redox reactions. Meanwhile, magnetron sputtering N-doped carbon cloth (N-CC) is used as a scaffold to enhance the electrical conductivity. The deliberately designed Co-Ni2P on N-CC (Co-Ni2P@N-CC) with a typical 3D interconnected architecture facilitates the formation of abundant solid-liquid-gas three-phase reaction interfaces inside the architecture. Furthermore, the rational catalyst/substrate interfacial interaction is capable of inducing a solvation-mediated pathway to form toroidal-Li2O2. The results show that the Co-Ni2P@N-CC based Li-O2 battery exhibits an ultra-low overpotential (0.73 V), enhanced rate performance (4487 mA h g-1 at 500 mA g-1) and durability (stable operation over 671 h). The pouch-type battery based on the Co-Ni2P@N-CC flexible electrode runs stably for 581 min in air without obvious voltage attenuation. This work verifies that heterogeneous atom doping and interface interaction can remarkably strengthen the performance of Li-O2 cells and thus pave new avenues towards developing high-performance metal-air batteries.
RESUMEN
The degradation of oxygen electrodes caused by oxygen species in lithium-oxygen (Li-O2) batteries deteriorates their energy efficiency and cyclability and seriously hinders their commercial application. To achieve high energy efficiency and long-term cycle life, gradient-porous ultrathin FeCo2S4 nanosheets on Ni foam (FeCo2S4@Ni) were deliberately designed as a noncarbonaceous freestanding oxygen electrode for Li-O2 batteries. Notably, the gradient-porous structure in FeCo2S4@Ni can offer sufficient active sites as well as mitigate polarization caused by the mass transfer during discharge and charge. The synergistic effect of the two transition metals, Fe2+ and Co3+, optimizes their d-band electronic structure and enhances the intrinsic activity of the oxygen electrode. Benefiting from the above merits, the FeCo2S4@Ni based Li-O2 battery demonstrates greatly increased discharge capacity (8001 mA h g-1), improved rate capability (with a high capacity of 4401 mA h g-1 at 500 mA g-1), and enhanced cycling stability (with a low overpotential of below 1 V after 109 cycles). Our work demonstrates that the battery performance can be improved by regulating the structure and composition of the oxygen electrode and provides a promising strategy for developing high performance Li-O2 batteries.
RESUMEN
NiFe-based transition metal oxide (NiFe-TMO) has been identified as an effective electrocatalyst for lithium-oxygen (Li-O2) batteries due to its superior catalytic activity for oxygen evolution reaction. Improving the bifunctional catalytic ability of NiFe-TMO is essential for the further performance improvement of Li-O2 batteries. Herein, we regulated the electronic structure of free-standing NiFe LDO nanosheets array via introducing foreign Co ion to improve its bifunctional catalytic activity in Li-O2 batteries. Combined with well-designed electrode architecture and the deliberately modified surface electronic structure, this strategy markedly alleviates polarization problem in terms of low overpotential (0.98 V), and the discharge voltage within 110 cycles remains stable at 2.89 V without significant attenuation. This study illustrates an intimate connection between electronic structure engineering and catalytic activity optimization that is critical for the rational design of Li-O2 batteries.