Flame Spray Pyrolysis Co3O4/CoO as Highly-Efficient Nanocatalyst for Oxygen Reduction Reaction

Abstract

The oxygen reduction reaction (ORR) is the rate-limiting reaction in the cathode side of fuel cells. In the quest for alternatives to Pt-electrodes as cathodes in ORR, appropriate transition metal oxide-based electrocatalysts are needed. In the present work, we have synthesized Co3O4 and CoO/Co3O4 nanostructures using flame spray pyrolysis (FSP), as electrocatalysts for ORR in acidic and alkaline media. A detailed study of the effect of (Co-oxide)/Pt ratio on ORR efficiency shows that the present FSP-made Co-oxides are able to perform ORR at very low-Pt loading, 0.4% of total metal content. In acid medium, an electrode with (5.2% Pt + 4.8% Co3O4), achieved the highest ORR performance (Jmax = 8.31 mA/cm2, E1/2 = 0.66 V). In alkaline medium, superior performance and stability have been achieved by an electrode with (0.4%Pt + 9.6% (CoO/Co3O4)) with ORR activity (Jmax = 3.5 mA/cm2, E1/2 = 0.08 V). Using XRD, XPS, Raman and TEM data, we discuss the structural and electronic aspects of the FSP-made Co-oxide catalysts in relation to the ORR performance. Cyclic voltammetry data indicate that the ORR process involves active sites associated with Co3+ cations at the cobalt oxide surface. Technology-wise, the present work demonstrates that the developed FSP-protocols, constitutes a novel scalable process for production of co-oxides appropriate for oxygen reduction reaction electrodes.

Dense Crystalline–Amorphous Interfacial Sites for Enhanced Electrocatalytic Oxygen Evolution

“…Electrochemically Active Surface Area Calculation: To measure the electrochemical double layer capacitance of the samples, the potential was swept with a span of 100 mV in non-faradaic region, and repeated three times at each of five different scan rates (40,60,80, 100, and 120 mV s −1 ). In these regions, the integrated charge should be due to the charging of the electrode-electrolyte double layer.…”

From Stochastic Self‐Assembly of Nanoparticles to Nanostructured (Photo)Electrocatalysts for Renewable Power‐to‐X Applications via Scalable Flame Synthesis

“…For instance, oxygen vacancies in spinel Co 3 O 4 electrocatalysts were generated by postsynthetic thermal, [ 171 ] Ar‐plasma [ 172,173 ] or NaBH 4 [ 174 ] treatments, while they could be one‐step, in situ generated using FSP. [ 175 ] Generation oxygen vacancies in FSP can be achieved by utilizing the ratio of the fuel and precursor to tune the amount of oxidative oxygen from the dispersion flux or the air entrainment. [ 62,63,176 ] An equivalence ratio (Φ), a dimensionless number, is often used as an indicator of the nature of the working atmospheres during a flame synthesis, and is defined as follows [ 121,177 ] where n fuel and n oxidant are molar quantity of the oxidant (oxygen dispersion) and fuel (liquid precursor), respectively.…”

“…The oxygen vacancies are reported to increase conductivity and create more defects of the catalysts, resulting in much higher current density and selectivity toward formate and syngas production. Similarly, Belles et al [ 175 ] controlled the ratio of fuel and oxygen dispersion to yield CoO/CO 3 O 4 in an O 2 ‐lean flame for oxygen reduction reaction at low‐Pt loading.…”

MIL‐100(Fe) Supported Pt−Co Nanoparticles as Active and Selective Heterogeneous Catalysts for Hydrogenation of 1,3‐Butadiene

“… [27] The peak at 780.7 eV is assigned to Co 3+ 2p 3/2 . [28] Meanwhile, two satellite peaks at 786.19 eV and 802.21 eV are assigned to the shakeup peaks of Co 2p 1/2 and Co 2p 3/2 . [27] Co is deeply oxidized to Co 3+ in Pt1Co1/MIL‐100(Fe) catalyst, which could be attributed to the influence of MIL‐100(Fe) environment.…”

“…The fitted Co 2p spectrum of Pt1Co1/MIL‐100(Fe) exhibits peaks at 782.0 eV (Co 2+ 2p 1/2 ) and 796.0 eV (Co 2+ 2p 3/2 ) [27] . The peak at 780.7 eV is assigned to Co 3+ 2p 3/2 [28] . Meanwhile, two satellite peaks at 786.19 eV and 802.21 eV are assigned to the shakeup peaks of Co 2p 1/2 and Co 2p 3/2 [27] .…”