Highly Active Hollow Porous Carbon Spheres@Graphite Felt Composite Electrode for High Power Density Vanadium Flow Batteries

Abstract

Improving power density is considered as one of the most effective methods to decrease the cost of vanadium flow batteries (VFBs). To reduce the polarization loss of VFBs, a hollow porous carbon sphere, whose inner and outer surfaces can both provide active sites catalyzing the redox reactions of vanadium redox couples, is designed and prepared by using nickel metal–organic framework (Ni‐MOF) as a template with the assistance of polyvinylpyrrolidone (PVP). This catalyst with its high specific surface area can be simply in situ loaded on the graphite felt forming a composite electrode. The composite electrode exhibits outstanding electrocatalytic activity, as the vanadium ions can participate in the reaction on both inner and outer surfaces of the hollow spheres. As a result, a VFB single cell assembled with this electrode can achieve a high energy efficiency of 82.7% at a current density of 200 mA cm−2 and a peak power density of 958 mW cm−2, which is much higher than those of pristine graphite felts. This work provides a new idea for the development of highly active electrocatalysts for VFBs and further improves the power density of a VFB.

CuCo2O4/NiCo-Metal–Organic Framework Nanoflake Arrays for High-Performance Supercapacitors

“…The peaks of CuCo 2 O 4 /NiCo-MOF can be divided into four fitting peaks that are located at 530.3, 530.9, 531.6, and 532.4 eV, corresponding to metal–oxygen bonds (M–O), oxygen defects, carboxyl groups (OC–O), and water in the sample. , In CuCo 2 O 4 , the peak at 531.7 eV corresponds to −OH, , and the other peaks are basically consistent with CuCo 2 O 4 /NiCo-MOF. From the O 1s peaks of NiCo-MOF, it can be clearly seen that, compared with CuCo 2 O 4 /NiCo-MOF and CuCo 2 O 4 , the binding energy of the M–O bond is higher (531.1 eV), which also occurs in other works that applied PTA as the MOF ligand, ,, indicating that the outer-layer electron density of the M–O bonds increases because of the introduction of organic ligands …”

“…Among them, the fitted peaks at 857.2 and 873.2 eV correspond to Ni 2+ and 856.0 and 874.5 eV correspond to Ni 3+ . The two peaks at 880.0 and 861.9 eV are satellite peaks of Ni 2p 1/2 and Ni 2p 3/2 , respectively. − The XPS spectrum of Cu in CuCo 2 O 4 /NiCo-MOF (Figure d) exhibits two main peaks of Cu 2p 3/2 and Cu 2p 1/2 at binding energies of 935.0 and 964.9 eV, confirming the presence of Cu 2+ that belongs to CuCo 2 O 4 . , In Figure e, the two main peaks of CuCo 2 O 4 /NiCo-MOF can be separated into two small peaks: the two peaks located at 781.3 and 797 eV correspond to Co 3+ , and the two peaks located at 783.3 and 798.6 eV are attributed to Co 2+ . The other peaks located at 786.7 and 803.2 eV are satellite peaks of Co 2p 3/2 and Co 2p 1/2 .…”

Flexible Carbon Sponge Electrodes for All Vanadium Redox Flow Batteries

“…Harvesting the electricity from sporadic renewable energy sources, including solar and wind, is expected to play a pivot role in meeting future energy demands [1–4] . However, effective utilization of the intermittent and fluctuated renewable electricity calls for reliable and powerful energy storage systems [5–10] . Redox flow batteries (RFBs) are among the leading technologies for storing electricity in large scales [11–13] .…”

“…[1][2][3][4] However, effective utilization of the intermittent and fluctuated renewable electricity calls for reliable and powerful energy storage systems. [5][6][7][8][9][10] Redox flow batteries (RFBs) are among the leading technologies for storing electricity in large scales. [11][12][13] Different from solidstate batteries, the energy-bearing species are usually dissolved in liquid electrolytes and stored outside the power-packs.…”

Synergetic Modulation on Solvation Structure and Electrode Interface Enables a Highly Reversible Zinc Anode for Zinc–Iron Flow Batteries

“…The current tendency in the utilization of sustainable energy prompts the development of efficient and stable energy storage systems. Of all energy storage technologies, redox flow batteries (RFBs) have attracted enormous interest as promising large-scale electrochemical energy storage devices owing to their unique features of flexible design in power and capacity, long cycle life, fast response, and no harmful emissions. − Although the state-of-the-art all-vanadium flow battery has reached full commercialization nowadays, − the high cost of the vanadium raw material greatly limits its wide deployment for applications, so there is an urgent need to develop alternative redox chemistries for aqueous flow batteries. Various metal-based, polysulfide-based, and organic RFBs have recently been proposed in the literature, − among which zinc-based have RFBs received the most attention and promise very tempting alternatives to the all-vanadium RFBs because of their excellent combination of low cost, high solubility, and environmental friendliness. − …”