Influence of Non-Conducting Zirconia on the Electrochemical Performance of Nickel Oxide in Alkaline Media at Room Temperature

Abstract

A composite of nickel(II) oxide and tetragonal-phase zirconia was synthesized using a co-precipitation technique and its performance as a bifunctional electrocatalyst in carbonate alkaline media at room temperature was examined. It was found that the non-conducting tetragonal-phase zirconia was active to adsorb carbonate anions, abstract oxygen and donate activated oxygen species to nickel oxide. NiO provided electronic conductivity and electrocatalytically active sites to facilitate the partial oxidation of methane to oxygenates at room temperature. This discovery of oxidation reactions utilizing carbonate anions could potentially open the door to new avenues of research for alternative alkaline electrochemical cells operating at low temperature with CO 3 2− as the transport ion.

Ultrahigh Electrocatalytic Conversion of Methane at Room Temperature

“…As detailed in a previous study, formaldehyde should be the methanol oxidation product. [23] After comparing the amount of ethanol and acetaldehyde (products containing two carbon atoms), acetaldehyde can be confirmed as the main product from the addition reaction of CH 4 and formaldehyde. Moreover, the amount of acetaldehyde decreased with the reaction time, which illustrates that acetaldehyde plays a pivotal role in the production of 1-propanol and 2-propanol, indicating that 1-propanol and 2-propanol were converted from acetaldehyde.…”

“…The formation of 2-propanol is common and has been reported in previous work. [23] As shown in Figure 5a, the methyl group in CH 4 acts as a nucleophilic reagent and attacks the carbonyl carbon in acetaldehyde. Then, a nucleophilic addition reaction occurs to form 2-propanol as one of the main products in this CH 4 conversion reaction.…”

“…[20] By contrast, carbonate (CO 3 2− ) oxidizes species by donating a charged oxygen atom accompanied by CO 2 release, resulting in a large enthalpy of reaction and favorable oxidation kinetics. [21][22][23] Therefore, CO 3 2− may be an attractive alternative to OH − for alkaline electrochemical reactions. In addition, to realize the donation of an oxidizing agent from CO 3 2− , zirconia (ZrO 2 ) should be employed to facilitate CO 3 2− adsorption because of its surface Lewis acid sites and electronaccepting capabilities.…”

Conversion of Methane into Liquid Fuels—Bridging Thermal Catalysis with Electrocatalysis

“…Metal oxides, such as NiO and Co 2 O 3 , are inactive thermal catalysts but are active for electrocatalytic methane oxidation. [112][113][114] This phenomenon could be explained by the changes in the metal oxidation states and surface free energies by electrode potential, resulting in a nonequilibrium population of a highly reactive MO sites. The high-energy MO sites are difficult to form thermochemically using O 2 (i.e., high G f ), but they can be generated by applying an anodic potential.…”

“…The high-energy MO sites are difficult to form thermochemically using O 2 (i.e., high G f ), but they can be generated by applying an anodic potential. [29] Ni(OH) 2 , [112] NiO/ ZrO 2 , [113,114] and Co 2 O 3 /ZrO 2 [115] have been explored as anode catalysts for methane activation at room temperature in carbonate electrolyte. The generation of methanol and higher alcohols such as propanol was observed by 1 H NMR or MS, but the TOF, TON, and Faradic efficiency were not qualified possibly due to the low yield.…”