Multi‐Functional Cerium Modification to Accelerate the Oxygen Reduction Reaction of Spinel Co₃O₄

Abstract

To enhance the oxygen reduction reaction (ORR) activity of spinel Co 3 O 4 , in this work, a novel strategy of cerium (Ce) modification is developed via the co-precipitation and followed annealing method. The Ce modification not only diminishes the critical size, but also increases the surface content of Co 3 + and elevates the conductivity of the Co 3 O 4 electrocatalysts, working together to enhance the ORR activity. Moreover, the adsorptive CeO 2 on the surface of Co 3 O 4 further promotes the ORR activity by the synergistic effect between CeO 2 and Co 3 O 4 . Typically, the optimized 0.5 % CeÀ Co 3 O 4 exhibits a half-wave potential of 0.665 V versus reversible hydrogen electrode (RHE) and low Tafel slope of À 60 mV dec À 1 as well as long-term stability.

Ce-modified Co–Mn oxide spinel on reduced graphene oxide and carbon black as ethanol tolerant oxygen reduction electrocatalyst in alkaline media

“…In fact, the doped Ce can regulate the geometrical and electronic structure and thus improve the ability to adsorb oxygen and provide more active sites and, at the same time, the synergistic effects between CMO and CeO 2 , which acts as an “oxygen buffer”, have a positive effect. 17,18,22,30…”

“…14,15,22,30 In addition, the synergistic effects of CeO 2 and CMO contribute positively to ORR performance, because Ce acts as a so-called “oxygen buffer” ensuring oxygen activation and oxygen enrichment, while also enhancing the binding energy for intermediate oxygenated adsorbates. 15–18,22,29…”

“…6,9 In addition, the slightly shied diffraction peaks of Ce-CMO samples compared to pure CMO can indicate the substitution of Co ions with larger ions (Mn and Ce ions) on the octahedral/tetrahedral sites, implying a high Mn content and Ce incorporation into the spinel structure. 6,22 According to the literature, 22,42,45 it is presumed that the Ce ions with large ionic radii are preferably placed on the larger octahedral interstices, and thus cause an increase in the lattice parameters and d-spacing. The XRD patterns of Ce-CMO/VC and Ce-CMO/rGO-VC further conrm the presence of the CeO 2 crystal structure in addition to the spinel phase.…”

“…Numerous studies in which cobalt or manganese oxides were either doped with cerium in the crystal and/or CeO 2 was generated for synergistic effects reveal an improvement in electrocatalytic activity. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] For example, Wang et al 22 found that Ce doping and CeO 2 decoration of Co 3 O 4 results in a higher ORR activity attributed to decreased particle size, enhanced conductivity, a higher Co 3+ /Co 2+ ratio and the synergetic interaction between CeO 2 and Co 3 O 4 . These effects can be related to the exible transition in the Ce 3+ /Ce 4+ redox couple and the existing 4f orbital of Ce facilitates electron transfer and provides active sites.…”

Porous spinel-type transition metal oxide nanostructures as emergent electrocatalysts for oxygen reduction reactions

“…101 The modification of Co 3 O 4 with Ce (Ce-Co 3 O 4 ) was achieved by a co-precipitation method and annealing, where optimized 0.5% Ce adsorption on Co 3 O 4 (i.e., 0.5% Ce-Co 3 O 4 ) reduced its critical size, and increased the Co 3+ surface content and conductivity for boosted ORR activity and stability. 102 The effect of temperature (70, 90, 120 and 150 °C) on the sizes and morphology of MnCoO was investigated for the ORR. 103 MnCoO-90 NCs possessed superior ORR kinetics compared with E onset , E 1/2 and J L (−0.18 V; −0.25 V vs. Ag/AgCl; 5.3 mA cm −2 ), while MnCoO-70, MnCoO-120 and MnCoO-150 had an E onset in the range −0.20 to −0.22 V vs. Ag/ AgCl, and an E 1/2 of −0.28 to −0.29 V vs. Ag/AgCl.…”