Correlating the crystal structure and facet of indium oxides with their activities for CO2 electroreduction.

Constructing structure-function relationships is critical for the rational design and development of efficient catalysts for CO2 electroreduction reaction (CO2RR). In2O3 is well-known for its specific ability to produce formic acid. However, how the crystal phase and surface affect the CO2RR activity is still unclear, making it difficult to further improve the intrinsic activity and screen for the most active structure. In this work, cubic and hexagonal In2O3 with different stable surfaces ((111) and (110) for cubic, (120) and (104) for hexagonal) are investigated for CO2RR. Theoretical results demonstrate that the adsorption of reactants on cubic In2O3 is stronger than that on hexagonal In2O3, with the cubic (111) surface being the most active for CO2RR. In experiments, synthesized cubic In2O3 nanosheets with predominantly exposed (111) surfaces exhibited a high HCOO- Faradaic efficiency (87.5%) and HCOO- current density (-16.7 mA cm-2) at -0.9 V vs RHE. In addition, an aqueous Zn-CO2 battery based on a cubic In2O3 cathode was assembled. Our work correlates the phases and surfaces with the CO2RR activity, and provides a fundamental understanding of the structure-function relationship of In2O3, thereby contributing to further improvements in its CO2RR activity. Moreover, the results provide a principle for the directional preparation of materials with optimal phases and surfaces for efficient electrocatalysis.

In Situ Symbiosis of Cerium Oxide Nanophase for Enhancing the Oxygen Electrocatalysis Performance of Single-Atom Fe─N─C Catalyst with Prolonged Stability for Zinc-Air Batteries.

The Fenton reaction, induced by the H2O2 formed during the oxygen reduction reaction (ORR) process leads to significant dissolution of Fe, resulting in unsatisfactory stability of the iron-nitrogen-doped carbon catalysts (Fe-NC). In this study, a strategy is proposed to improve the ORR catalytic activity while eliminating the effect of H2O2 by introducing CeO2 nanoparticles. Transmission electron microscopy and subsequent characterizations reveal that CeO2 nanoparticles are uniformly distributed on the carbon substrate, with atomically dispersed Fe single-atom catalysts (SACs) adjacent to them. CeO2@Fe-NC achieves a half-wave potential of 0.89 V and a limiting current density of 6.2 mA cm-2, which significantly outperforms Fe-NC and commercial Pt/C. CeO2@Fe-NC also shows a half-wave potential loss of only 1% after 10 000 CV cycles, which is better than that of Fe-NC (7%). Further, H2O2 elimination experiments show that the introduction of CeO2 significantly accelerate the decomposition of H2O2. In situ Raman spectroscopy results suggest that CeO2@Fe-NC significantly facilitates the formation of ORR intermediates compared with Fe-NC. The Zn-air batteries utilizing CeO2@Fe-NC cathodes exhibit satisfactory peak power density and open-circuit voltage. Furthermore, theoretical calculations show that the introduction of CeO2 enhances the ORR activity of Fe-NC SAC. This study provides insights for optimizing SAC-based electrocatalysts with high activity and stability.

Reconstructed Bismuth Oxide through in situ Carbonation by Carbonate-containing Electrolyte for Highly Active Electrocatalytic CO2 Reduction to Formate.

The catalyst-reconstruction makes it challenging to clarify the practical active sites and unveil the actual reaction mechanism during the CO2 electroreduction reaction (CO2 RR). However, currently the impact of the electrolyte microenvironment in which the electrolyte is in contact with the catalyst is overlooked and might induce a chemical evolution, thus confusing the reconstruction process and mechanism. In this work, the carbonate adsorption properties of metal oxides were investigated, and the mechanism of how the electrolyte carbonate affect the chemical evolution of catalysts were discussed. Notably, Bi2 O3 with weak carbonate adsorption underwent a chemical reconstruction to form the Bi2 O2 CO3 /Bi2 O3 heterostructure. Furthermore, in situ and ex situ characterizations unveiled the formation mechanism of the heterostructure. The in situ formed Bi2 O2 CO3 /Bi2 O3 heterostructure with strong electron interaction served as the highly active structure for CO2 RR, achieving a formate Faradaic efficiency of 98.1 % at -0.8 Vvs RHE . Theoretical calculations demonstrate that the significantly tuned p-orbit electrons of the Bi sites in Bi2 O2 CO3 /Bi2 O3 optimized the adsorption of the intermediate and lowered the energy barrier for the formation of *OCHO. This work elucidates the mechanism of electrolyte microenvironment for affecting catalyst reconstruction, which contributes to the understanding of reconstruction process and clarification of the actual catalytic structure.

Promoting Electrocatalytic Reduction of CO2 to C2 H4 Production by Inhibiting C2 H5 OH Desorption from Cu2 O/C Composite.

The electrochemical CO2 reduction reaction (CO2 RR) has great potential in realizing carbon recycling while storing sustainable electricity as hydrocarbon fuels. However, it is still a challenge to enhance the selectivity of the CO2 RR to single multi-carbon (C2+ ) product, such as C2 H4 . Here, an effective method is proposed to improve C2 H4 selectivity by inhibiting the production of the other competitive C2 products, namely C2 H5 OH, from Cu2 O/C composite. Density functional theory indicates that the heterogeneous structure between Cu2 O and carbon is expected to inhibit C2 H5 OH production and promote CC coupling, which facilitates C2 H4 production. To prove this, a composite electrode containing octahedral Cu2 O nanoparticles (NPs) (o-Cu2 O) with {111} facets and carbon NPs is constructed, which experimentally inhibits C2 H5 OH production while strongly enhancing C2 H4 selectivity compared with o-Cu2 O electrode. Furthermore, the surface hydroxylation of carbon can further improve the C2 H4 production of o-Cu2 O/C electrode, exhibiting a high C2 H4 Faradaic efficiency of 67% and a high C2 H4 current density of 45 mA cm-2 at -1.1 V in a near-neutral electrolyte. This work provides a new idea to improve C2+ selectivity by controlling products desorption.

Inert chemical looping conversion of biochar with iron ore as oxygen carrier: Products conversion kinetics and structural evolution.

In this study, biochar obtained from pyrolysis of woody shavings at 550 °C was reacted with iron ore in N2 to investigate its inert chemical looping conversion properties, including the gas products conversion kinetics and structural evolution process. Results found that both the release of CO and CO2 could be divided into rapid release stage and stable chemical looping reaction stage with activation energies of 17.69 and 45.65 kJ/mol, respectively. During the chemical looping process, the reaction reactivity of biochar reduced gradually with the amorphous char structure turning into fused ring structure and finally into graphite crystal structure. Simultaneously, Fe2O3 was reduced into Fe3O4, FeO and Fe. This work highlighted the chemical conversion of biochar using natural iron ore as oxygen carrier in inert N2 atmosphere from the common in-situ gasification chemical looping process using CO2/H2O as agent.