Oxygen-Vacancy-Rich Cubic CeO₂ Nanowires as Catalysts for Vanadium Redox Flow Batteries

Abstract

A novel, low-cost, and powerful cerium-oxide nanowire (CeO2NW) electrode decorated with graphite felt (GF) through a one-step hydrothermal method was proposed in this study. Subsequently, hydrogen annealing was conducted to create defective-hydrogen-annealed CeO2NWs decorated with GF (H–CeO2NWs–GF) for use in vanadium redox flow batteries (VRFBs). The electrochemical results show that the H–CeO2NWs–GF reveals excellent electrocatalytic effects toward the VO2 +/VO2+ redox process in VRFBs at the positive electrode to facilitate the electrochemical kinetics of the VRFBs. The VRFBs using different electrode materials were compared with a VRFB using H–CeO2NWs–GF. The results revealed that the VRFB using H–CeO2NWs–GF exhibits the highest voltage efficiency of 90.4% at a current density of 40 mA cm–2, which is significantly higher than those using pristine GF (81.1%) and a CeO2NW electrode decorated with GF (88.4%). The significant improvement in the electrochemical performance of H–CeO2NWs–GF might be mostly ascribed to the defect-rich H–CeO2NWs on the GF surface, which acts as active sites and reduces the electrochemical polarization of the redox reaction. Moreover, the one-dimensional nature of H–CeO2NWs is favorable for the charge-transfer process and improves the accessibility, thus improving the electrode performance.

Synergistic Catalysis of SnO2-CNTs Composite for VO2+/VO2+ and V2+/V3+ Redox Reactions

“…Regarding metal catalysts [e.g., Cu (Wei et al, 2016), Ir (Wang et al, 2007) and Sb (Kou et al, 2020)], Zhou et al (2020) used semi-embedded carbon felt with bismuth nanospheres, which had good catalytic activity and could effectively promote the redox reaction of the negative electrode. For metal oxides [e.g., Nd 2 O 3 (Fetyan et al, 2018), MnO 2 (Ma et al, 2018), and PbO 2 (Wu et al, 2014)], Bayeh et al (2020) (Etesami et al, 2018)], Park et al (2013) demonstrated that carbon nanofiber/nanotube composite catalysts had good electrocatalytic performance in VRFB. Compared with the untreated electrode, the discharge capacity of the modified electrode increased by 64% at 40 mA cm −2 .…”

“…Regarding metal catalysts [e.g., Cu (Wei et al, 2016 ), Ir (Wang et al, 2007 ) and Sb (Kou et al, 2020 )], Zhou et al ( 2020 ) used semi-embedded carbon felt with bismuth nanospheres, which had good catalytic activity and could effectively promote the redox reaction of the negative electrode. For metal oxides [e.g., Nd 2 O 3 (Fetyan et al, 2018 ), MnO 2 (Ma et al, 2018 ), and PbO 2 (Wu et al, 2014 )], Bayeh et al ( 2020 ) modified GF with cubic CeO 2 nanowires and used it as a catalyst for VRFB. This resulted in abundant defects on the electrode surface and increased active sites, meaning that the CeO 2 nanowires could significantly improve the /VO 2+ redox process.…”

Controlled Metal–Support Interactions in Au/CeO2–Mg(OH)2 Catalysts Activating the Direct Oxidative Esterification of Methacrolein with Methanol to Methyl Methacrylate

“…Pure MgO without the addition of CeO 2 (Ce:Mg = 0:100) exhibited distinct XRD reflections corresponding to a cubic lattice with (111), (200), and (220) planes (hkl indices in black in Figure 1A) [29]. As the amount of Ce precursor increased in the synthesis gel composition, with a corresponding decrease in Mg precursor, the XRD peak intensities for MgO decreased gradually, and the XRD reflections corresponding to the cubic structure of CeO 2 , with different lattice parameters, became more prominent (hkl indices in red in Figure 1A) [30]. The mixed phases of CeO 2 and MgO with controlled gel composition during synthesis were characterized by the Rietveld refinement, which quantitatively analyzed the composition ratio of CeO 2 and MgO as summarized in Table 1 [31][32][33][34].…”

Metal-Organic Frameworks Derived Catalyst for High-Performance Vanadium Redox Flow Batteries

“…However, these noble metals have lower elemental abundance and higher costs. To diminish the costs, cheap metal oxides such as Nb 2 O 5 [8], Ta 2 O 5 [9], W 18 O 49 [10], and CeO 2 [11] have been studied and exhibited good electrocatalytic activity. However, since the transition metal cations present several oxidative states, they make oxidation and reduction reactions carry on poor electronic conductivity and hinder the charge transfer efficiency from the catalysts to electrodes.…”