Composition‐Dependent Effect of the Calcination of Cobalt‐, Nickel‐, and Gallium‐Based Layered Double Hydroxides to Mixed Metal Oxides in the Oxygen Evolution Reaction

Abstract

Mixed cobalt and nickel based layered double hydroxides (LDHs) with Ga as the third cation and the mixed metal oxides (MMOs) resulting from their thermal decomposition were synthesized in various compositions through constant pH coprecipitation and calcination. The structural and textural properties of the catalysts with variable Co/Ni ratios were assessed by N 2 physisorption, powder X-ray diffraction, and electron microscopy. The obtained materials exhibit electrocatalytic activity for the oxygen evolution reaction in alkaline solution. The highest activity was found for catalysts containing both transition-metal cations, Co and Ni. However, comparison of the LDH precursors and the calcined MMOs revealed a composition-dependent effect of calcination. Co-rich LDH tends to lose activity when calcined, whereas Ni-rich LDH gains activity. The optimal cation composition of the LDH was Co 1.5 Ni 0.5 Ga with an overpotential of 382 mV. The highest performance among the MMOs, on the other hand, has been encountered for the Co 0.5 Ni 1.5 Ga composition, reaching a similar overpotential.

Promotion Effect of Ga−Co Spinel Derived from Layered Double Hydroxides for Toluene Oxidation

“…Therefore, we preferred to assign the XRD patterns to the combination or mixture of these spinel species. The similar results were also reported in previous works ,,. Meanwhile, the average crystallite sizes of all samples were calculated by X‐ray diffraction with the Scherrer equation.…”

“…For Al−Co spinel, all the peaks for Al−Co spinel between the standard peaks of AlCo 2 O 4 , Al 2 CoO 4 and Co 3 O 4 , these peaks can be indexed to the spinel oxide phases (Co 2 AlO 4 , JCPDS 38–0814; CoAl 2 O 4 , JCPDS 44–0160; Co 3 O 4 , JCPDS 74–2120) ,. All the peaks for Ga−Co spinel and Ga−Co sol‐gel are between the standard peaks of Ga 2 CoO 4 and Co 3 O 4 , which were attributed to the mixed spinel oxide phases (CoGa 2 O 4 , JCPDS 11–0698; Co 3 O 4 , JCPDS 74–2120) . But we cannot assign these peaks to the specific phases of spinel, because several spinel phases (AlCo 2 O 4 , Al 2 CoO 4 , CoGa 2 O 4 and Co 3 O 4 ) have the relatively close XRD peak positions.…”

“…Alternatively, Ga−Co spinel is a highly efficient electrochemical catalyst because of the existence of oxygen vacancies . Recently, the mixed spinel oxides that containing Co, Ni and Ga, have different Co/Ni ratios, and implement Ga as the trivalent metal cations derived from LDH, demonstrate higher capacitance during the oxygen evolution reaction . In addition, the structures and properties of the obtained spinel oxides can be modified by altering the composition of the LDH precursors .…”

Enhanced Water Oxidation Activity by Introducing Gallium into Cobalt‐Iron Oxide System

“…They ascribed the enhanced OER activity to the formation of coordination‐unsaturated CoO 6‐x units in CoGa LDH . Behrens et al found that Co 1.5 Ni 0.5 Ga LDH showed an overpotential of 382 mV in 1 M KOH solution . Nener et al used density functional theory calculations to reveal that the over potential on the (−201) β‐Ga 2 O 3 surface is very high .…”

Electrochemical Growth of Mg(OH)x Layered Films Stacked Parallel to the Substrates and Their Thermal Conversion to (111)-Oriented Nanoporous MgO Films

“… 1 − 6 LMHs also act as a valuable precursor to yield unique nanostructured materials, e.g., two-dimensional (2D) hydroxide thin films by exfoliation and nanoporous oxides by thermal decomposition. 7 − 10 …”