Plasma-assisted defect engineering of N-doped NiCo2O4 for efficient oxygen reduction

Plasma-Engineering of Oxygen Vacancies on NiCo2O4 Nanowires with Enhanced Bifunctional Electrocatalytic Performance for Rechargeable Zinc-air Battery

Designing an efficient, durable, and inexpensive bifunctional electrocatalyst toward oxygen evolution reactions (OER) and oxygen reduction reactions (ORR) remains a significant challenge for the development of rechargeable zinc-air batteries (ZABs). The generation of oxygen vacancies plays a vital role in modifying the surface properties of transition-metal-oxides (TMOs) and thus optimizing their electrocatalytic performances. Herein, a H2/Ar plasma is employed to generate abundant oxygen vacancies at the surfaces of NiCo2O4 nanowires. Compared with the Ar plasma, the H2/Ar plasma generated more oxygen vacancies at the catalyst surface owing to the synergic effect of the Ar-related ions and H-radicals in the plasma. As a result, the NiCo2O4 catalyst treated for 7.5 min in H2/Ar plasma exhibited the best bifunctional electrocatalytic activities and its gap potential between Ej = 10 for OER and E1/2 for ORR is even smaller than that of the noble-metal-based catalyst. In situ electrochemical experiments are also conducted to reveal the proposed mechanisms for the enhanced electrocatalytic performance. The rechargeable ZABs, when equipped with cathodes utilizing the aforementioned catalyst, achieved an outstanding charge-discharge gap, as well as superior cycling stability, outperforming batteries employing noble-metal catalyst counterparts.

Defect Engineering for Enhanced Electrocatalytic Oxygen Reaction on Transition Metal Oxides: The Role of Metal Defects

Metal defect engineering is a highly effective strategy for addressing the prevalent high overpotential issues associated with transition metal oxides functioning as dual-function commercial oxygen reduction reaction/oxygen evolution reaction catalysts for increasing their activity and stability. However, the high formation energy of metal defects poses a challenge to the development of strategies to precisely control the selectivity during metal defect formation. Here, density functional theory calculations are used to demonstrate that altering the pathway of metal defect formation releases metal atoms as metal chlorides, which effectively reduces the formation energy of defects. The metal defects on the monometallic metal oxide surface (Mn, Fe, Co, and Ni) are selectively produced using chlorine plasma. The characterization and density functional theory calculations reveal that catalytic activity is enhanced owing to electronic delocalization induced by metal defects, which reduces the theoretical overpotential. Notably, ab initio molecular dynamics calculations, ex situ XPS, and in situ ATR-SEIRAS suggest that metal defects effectively improve the adsorption of reactive species on active sites and enhance the efficiency of product desorption, thereby boosting catalytic performance.

Cold plasma synthesis of phosphorus-doped CoFe2O4 with oxygen vacancies for enhanced OER activity

Spinel-type metal oxides are promising electrocatalysts for the oxygen evolution reaction (OER) due to their unique electronic structure and low cost. Herein, we induced oxygen vacancies and doped phosphorus into CoFe2O4 using cold plasma. The abundant oxygen vacancies enhanced hydrophilicity and modified the electronic structure of CoFe2O4, while the phosphorus doping formed numerous new active centers. The doped P and formed FeP promoted the charge transfer and improved the conductivity of the catalyst. The phosphorus-doped CoFe2O4 exhibited exceptional OER activity with an overpotential of 180 mV at 10 mA cm-2 and a Tafel slope of 65.8 mV dec-1 in an alkaline electrolyte. DFT calculations confirmed that phosphorus doping can improve the charge distribution near the Fermi level and optimize the d-band center position.

Starch-based porous carbon microsphere composited NiCo2O4 nanoflower as bifunctional electrocatalyst for zinc-air battery

It is significant to explore and design outstanding bifunctional oxygen electrocatalysts to promote the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in zinc-air batteries. Herein, a novel porous carbon microspheres (CMS₂) modified by NiCo₂O₄ nanoflower (CMS₂-NiCo₂O₄) has been prepared as an ORR and OER catalyst. The hierarchical porous structure of CMS provides high conductivity and abundant active sites for ORR, whereas the synergistic effect of NiCo₂O₄ nanosheets and a small amount of FeZn oxides act as the positive phase for OER. The efficient oxygen catalytic activity is gained by creating a coupling interface between NiCo₂O₄ and CMS. The optimized CMS₂-NiCo₂O₄ shows a half-wave potential of 0.82 V toward ORR and an overpotential of 392 mV toward OER. Particularly, CMS₂-NiCo₂O₄ also exhibits an excellent peak power density (175.5 mW cm^-2) as a catalyst for zinc-air batteries, which is superior to the commercial Pt/C + RuO₂ catalyst (120.5 mW cm^-2), and it also demonstrates a remarkable stability even after the charge-discharge cycles of 167 h. The prepared CMS₂-NiCo₂O₄ is promising for the application of the bimetallic oxide catalyst for zinc-air battery.

Facile synthesis of multiphase cobalt-iron spinel with enriched oxygen vacancies as a bifunctional oxygen electrocatalyst

The multiphase cobalt-iron spinel was firstly synthesized via a facile cold plasma method and applied as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Compared with the single-phase obtained by the traditional calcination method, the CoFe₂O₄ and Co₃O₄ phase were obtained by the plasma method. The multivalence states of cobalt and iron facilitated electron transport in electrochemical reactions. The plasma sample had a small particle size (5 nm) due to the low operation temperature. Notably, electron impact produced more oxygen vacancies and a larger surface area on Co_xFe_yO₄, which increased the active sites and electronic conductivity. Electrochemical investigations indicated that the multiphase spinel obtained with a quasi-four-electron transfer process showed an onset potential of 0.76 V versus the RHE for the oxygen reduction reaction. In the oxygen evolution reaction, the potential of current density at 10 mA cm^-2 was 1.53 V versus RHE. As for the overall electrocatalytic activity, the multiphase spinel had a ΔE (the difference between E₁₀(OER) and E_1/2(ORR)) of 0.89 V, exhibiting greater bifunctional activity than the other prepared catalysts.

Synergic fabrication of pembrolizumab loaded doxorubicin incorporating microbubbles delivery for ultrasound contrast agents mediated anti-proliferation and apoptosis

This study evaluated pembrolizumab-conjugated, doxorubicin (DOX)-loaded microbubbles (PDMs) in combination with ultrasound (US) as molecular imaging agents for early diagnosis of B cell lymphomas, and as a targeted drug delivery system. Pembrolizumab, a monoclonal CD20 antibody, was attached to the surfaces of DOX-loaded microbubbles. PDM binding to B cell lymphoma cells was assessed using immunofluorescence. The cytotoxic effects of PDMs in combination with ultrasound (PDMs + US) were evaluated in vitro in CD20+ and CD20– cell lines, and its antitumor activities were assessed in Raji (CD20+) and Jurkat (CD20–) lymphoma cell-grafted mice. PDMs specifically bound to CD20+ cells in vitro and in vivo. Contrast enhancement was monitored in vivo via US. PDM peak intensities and contrast enhancement durations were higher in Raji than in Jurkat cell-grafted mice (p < 0.05). PDMs + US treatment resulted in improved antitumor effects and reduced systemic toxicity in Raji cell-grafted mice compared with other treatments (p < .05). Our results showed that PDMs + US enhanced tumor targeting, reduced systemic toxicity, and inhibited CD20+ B cell lymphoma growth in vivo. Targeted PDMs could be employed as US molecular imaging agents for early diagnosis, and are an effective targeted drug delivery system in combination with US for CD20+ B cell malignancy treatment.