1669 Korean J. Chem. Eng., 37(10), 1669-1679 (2020) DOI: 10.1007/s11814-020-0571-9 INVITED REVIEW PAPER pISSN: 0256-1115 eISSN: 1975-7220 INVITED REVIEW PAPER † To whom correspondence should be addressed. E-mail: z_yavari@chem.usb.ac.ir, m.noroozifar@utoronto.ca Copyright by The Korean Institute of Chemical Engineers. Electrooxidation of single-carbon molecules by nanostructured Pd-decorated spongy ceria Zahra Yavari * , ** ,† , Mahdi Shafiee Afarani *** , Amir Masoud Arabi **** , and Meissam Noroozifar ***** ,† *Department of Chemistry, University of Sistan and Baluchestan, P.O. Box 98135-674, Zahedan, Iran **Renewable Energies Research Institute, University of Sistan and Baluchestan, Zahedan, Iran ***Department of Materials Engineering, Faculty of Engineering, University of Sistan and Baluchestan, Zahedan, Iran ****Department of Inorganic Pigments and Glazes, Institute for Color Science and Technology (ICST), Tehran, Iran *****Department of Physical and Environmental Sciences, University of Toronto Scarborough 1265 Military Trail, Toronto, Ontario, M1C 1A4, Canada (Received 24 December 2019 • Revised 9 May 2020 • Accepted 11 May 2020) AbstractSolution combustion synthesis is proposed to fabricate spongy ceria by using two different fuels for com- bustion: glycine and urea. As-prepared samples are labeled as SCO Gl and SCO Ur . The acid-base properties of the cavi- ties and surfaces of specimens are determined by measuring the pH of zero charges. Both SCO Gl and SCO Ur powders are decorated by the nanostructured Pd (NSPd) by the wetness incorporation. The NSPd-SCO Gl and NSPd-SCO Ur rep- resent the high mass current density than NSPd as non-supported palladium for the electrooxidation of single-carbon molecules: methanol, formaldehyde and formic acid. The results show that the NSPd-SCO Gl and NSPd-SCO Ur are exceptional heterogeneous catalysts. The SCO as the support with porous structural network has been affected consid- erably on the electrochemical surface area, dispersion, and durability of NSPd. On the other hand, it can be effective for removing the poisoning species of the electrooxidation of single-carbon molecules on NSPd through the lattice oxy- gen, and the activation of an oxidation-reduction cycle between the high and low chemical valences of cerium, leading to improve the electrocatalytic efficiency of NSPd. Finally, it is confirmed the conversion of methanol to formaldehyde, and then to formic acid during electrooxidation by using cyclic voltammetry studies. Keywords: Single-carbon Molecules, Solution Combustion Synthesis, Methanol, Electrocatalyst, Cerium (IV) Oxide INTRODUCTION The electrooxidation of organic compounds is widely connected with the progress of fuel cells and the electrochemical sensors [1- 4]. It is an electrocatalytic reaction proceeding over electron trans- fers and is intricate via the molecule adsorption on the surface of heterogeneous catalyst and creation of poisoning intermediate. Such reactions are great electrocatalyzed on noble metals [5,6] with great ability toward dehydrogenation molecules, as well as one provid- ing oxygen species [7]. Succinctly, it may be essential to progress the transport kinetics of electron in electrocatalysts to increase the electrocatalysts activity. Currently, the support materials are considered [8-10], because they restrain the agglomerating noble metals and create a stable structure with high surface area efficiently; also, they have encour- aging electronic and geometric properties to advance the interac- tion among particles of noble metals and electrode surface, resulting in the improvement of electrocatalytic abilities [11]. To improve the dispersion of noble metals, carbon materials are frequently stud- ied as electrocatalyst supports [12,13]. Despite the high conduction coefficient of the carbon structures, current electrocatalysts still suf- fer from low utilization of noble metal, incomplete mass transport- ability, and the confined electrochemical stability of the carbon- based supports [14]. Hence, due to different properties like slight thermal conductivity, great thermal stability, and significant resis- tance to degradation for ceramic materials [15], they have attracted much attention to be available support for catalytic materials. The structural stability and feasibility of charge propagation are two key factors for the dispersion of noble metals in electrocatalysts in the support selection. Up to now, some ceramic structures are utilized in the catalytic electrooxidation of organic compounds, such as WO 3 [16], TiO 2 [7,17], SnO 2 [18,19], SiO 2 [20], Ti 0.5 Cr 0.5 N [21] and NiCo 2 O 4 [22]. Electrocatalytic materials with diverse morpholo- gies or structures possess distinct behaviors. Therefore, materials with similar composition and different morphologies have been stud- ied in the literature [23-25]. In the recent decade, porous materials have attracted more consideration owing to their specific skeletal feature, superior surface area, and the controllable cavity size. Also, they supply a short pathway to transport electrons and ions, con- sequently leading to rapid process kinetics. On the other hand, it is confirmed the efficiency of transition metal oxides is primarily man- aged through electrochemical behavior and kinetic characteristic of the active materials [26]. Although there are numerous literature researches on electro-cat- alysts introduction in the fuel cell, further study is essential. CeO 2 has been successfully employed as a compound of the catalytic com-