The three-dimensional (3D) distribution of individual atoms on the surface of catalyst nanoparticles plays a vital role in their activity and stability. Optimising the performance of electrocatalysts requires atomic-scale information, but it is difficult to obtain. Here, we use atom probe tomography to elucidate the 3D structure of 10 nm sized Co2FeO4 and CoFe2O4 nanoparticles during oxygen evolution reaction (OER). We reveal nanoscale spinodal decomposition in pristine Co2FeO4. The interfaces of Co-rich and Fe-rich nanodomains of Co2FeO4 become trapping sites for hydroxyl groups, contributing to a higher OER activity compared to that of CoFe2O4. However, the activity of Co2FeO4 drops considerably due to concurrent irreversible transformation towards CoIVO2 and pronounced Fe dissolution. In contrast, there is negligible elemental redistribution for CoFe2O4 after OER, except for surface structural transformation towards (FeIII, CoIII)2O3. Overall, our study provides a unique 3D compositional distribution of mixed Co-Fe spinel oxides, which gives atomic-scale insights into active sites and the deactivation of electrocatalysts during OER.

The La2O3 catalyst with a two-dimensional (2D) structure is more effective than 0D, 1D and 3D La2O3 for oxidative coupling of methane.

We fabricated Co 3 O 4 catalysts with different spatial structures, such as zero-dimensional (nanoparticles), one-dimensional (nanorods), two-dimensional (nanoplates), and three-dimensional (mesoporous and microporous) structures, for methane combustion. The Co 3 O 4 catalysts with different dimensional architectures demonstrated different activitiesf or the breaking of the CÀHb ond of methane. In particular, Co 3 O 4 with 2D structure gave rise to the highest activity amonga ll the samples, in which methanec ould be initially ignited below 200 8C and completely converted to CO 2 at 375 8C. This activity is attributed to the collective contribution from all the exposed high-index planes of 2D Co 3 O 4 andt om ore surface-active species being formed on 2D Co 3 O 4 .Natural gas is widely used in power generation,c hemicals, and vehicle fuels. The main component of natural gas,m ethane, is as ymmetrical molecule and av ery stable hydrocarbon.[1] Most methanec onversions are thermodynamically unfavorable at low temperatures owing to the positivea nd large value of the Gibbs free energy;t hus, ah igh reactiont emperature is generally required. The removal of methane from the environmenti s highly challenging for catalyst suppliers, as the high-temperature combustion leads to undesirable surface reactions and the emission of toxic nitrogen oxides (NO x )a nd CO.[2] Therefore, the developmento fa ctive catalysts forl ow-temperature methane combustion is crucial to remove methane from the environment and limit the emission of toxic gases.A lthough Pd is the best known methane combustion catalyst, [3] owing to the high cost of Pd and declining activity,a lternative catalysts based on non-noblem etals or metal oxides are being actively pursued. Many efforts have been made to obtain perovskite oxides, [4] hexaaluminates, [5] and transition metal oxides [2,6] for methane combustion at low temperature. Co 3 O 4 is one of the most intensively investigated transition metal oxides owing to its excellent performance in various catalytic processes, for example,C Oo xidation, [7] NO x reduction, [8] and the oxygen reduction reaction( ORR).[9] The properties of as-synthesized Co 3 O 4 mainlyd epend on its shape, surface structure, crystal phase, crystal size, and dimensionality.I th as been reported that, in the catalytic combustion of methane,C o 3 O 4 nanosheets enclosed by {112}p lanes exhibit highera ctivity than the corresponding nanobelts with exposed (0 11)f acets or nanocubes with exposed (0 01)f acets.[10] Co 3 O 4 nanotubes bounded by {112}p laness how excellent activity and good stability compared with Co 3 O 4 nanorods with exposed (110)f acets.[11] So far,however,Co 3 O 4 as aheterogeneous catalystwith controlled dimensionality hasr arely been mentioned in this catalytic reaction.In this work, to determine the spatial structuree ffect of Co 3 O 4 on methanec ombustion, we set out to synthesize Co 3 O 4 catalysts with fascinating architectures from 0D (dimensional) to 3D,s uch as nanoparticles (0 D), nanorods (1 D), ...