Electro-oxidation Reaction of Methanol over Reducible Ce_1–x–yNi_xSr_yO_2−δ: A Mechanistic Probe of Participation of Lattice Oxygen

Abstract

Methanol oxidation reaction crucially depends on the formation of −OOH species over the catalyst’s surface. Ni-based catalysts are by far the choice of materials, where the redox couple of Ni2+/Ni3+ facilitates the formation of −OOH species by surface reconstructions. However, it is challenging to oxidize Ni2+ as it generates charge-transfer orbitals near the Fermi energy level. One possible solution is to substitute Ni2+ with a reducible oxide support, which will not only facilitate the Ni2+ → Ni3+ oxidation but also adsorb oxygenated species like −OOH at a lower potential owing to its oxophilicity. This work shows with the help of structural and surface studies that the reducible CeO2 support in Ni and Sr co-doped Ce1–x–y Ni x Sr y O2−δ solid solution can easily facilitate Ni2+ → Ni3+ oxidation as well as evolution of lattice oxygen during the methanol oxidation reaction. While the Ni3+ species helped in formation of −OOH surface intermediates, the evolved lattice oxygen eased the CO oxidation process in order to bring out the better CO-tolerant methanol oxidation activity over Ce1–x–y Ni x Sr y O2−δ. The study shows the unique importance of the electronic interactions between the active site and support and involvement of lattice oxygen in the methanol oxidation reaction.

Unveiling the Mechanistic Significance of Reducibility and Lattice Oxygen Evolution in the Ce1–x–yZrxNiyO2−δ Catalyst for Methanol Electro-Oxidation

“…It should be noted that the MOR activity was also significantly better than our earlier reports (Figure S7). With optimum doping of Zr in Ce 0.6 Zr 0.35 Ni 0.05 O 2−δ , the current density was found to be highest with 13.12 mA cm –2 . The current density was reduced with further doping of Zr in Ce 0.4 Zr 0.55 Ni 0.05 O 2−δ (9.04 mA cm –2 ).…”

Electro-Oxidation Reaction of Methanol over La2–xSrxNi1–y(Mn/Fe/Co)yO4+δ Ruddlesden–Popper Oxides

“…Investigation was carried out to examine the influence of electrochemical surface area (ECSA) on the activity of MOR. The ECSA was calculated with the help of chrono-amperometric studies using the Cottrell equation Q = 2 n FAD 1/2 C o t 1/2 π –1/2 , as shown in Figure . In the equation, Q = charge in coulomb, F = Faraday constant, n = number of electrons being transferred, A = area of electrode in cm 2 , D = diffusion coefficient of [K 3 Fe­(CN) 6 ] (7.6 × 10 –6 cm 2 s –1 ), t = time (s), and C o = concentration of K 3 Fe­(CN) 6 in mol cc –1 .…”

“…Oxides of nickel (Ni) have emerged as extensively studied transition-metal oxides for electrocatalysis due to their advanced oxygen-ion conductivity, structural diversity, nontoxicity, reduced onset potential, and improved catalytic activity. Research has indicated that the electrocatalytic oxidation of methanol by Ni-based oxides are facilitated by the Ni 3+ /Ni 2+ redox couple, primarily due to the creation of highly active surface-intermediate species known as Ni–OOH. − …”

The role of reducibility vis-à-vis oxygen vacancies of doped Co3O4/CeO2 in the oxygen evolution reaction

“…16,17 We further substituted Ce with Sr (Co 3 O 4 /Ce 1− y Sr y O 2− δ ) to enhance the oxidizing power of CeO 2 as Sr with a lower oxidation potential is a judicious choice for ameliorating the redox behaviour of cerium and cobalt. 18–23 To further enhance the impact of oxygen vacancies, we partially substituted the cobalt sites with another transition metal, namely Cu (Co 3− x Cu x O 4 /Ce 1− y Sr y O 2− δ ). The substitution of cobalt with copper will elevate the oxidation state of cobalt.…”