Electrocatalysis of oxygen reduction on multi-walled carbon nanotube supported copper and manganese phthalocyanines in alkaline media

Ligand Isomerization Driven Electrocatalytic Switching

The prevailing view about molecular catalysts is that the central metal ion is responsible for the reaction mechanism and selectivity, whereas the ligands mainly affect the reaction kinetics. Here, we question this paradigm and show that ligands have a dramatic influence on the selectivity of the product. We show how even a seemingly small change in ligand isomerization sharply alters the selectivity of the well-researched oxygen reduction reaction (ORR) Co phthalocyanine catalyst from an indirect 2e- to a direct 4e- pathway. Detailed analysis reveals that intramolecular hydrogen-bond interactions in the ligand activate the catalytic Co, directing the oxygen binding and thus deciding the final product. The resulting catalyst is the first example of a Co-based molecular catalyst catalyzing a direct 4e- ORR via ligand isomerization, for which it shows an activity close to the benchmark Pt in an actual H2-O2 fuel cell. The effect of the ligand isomerism is demonstrated with different central metal ions, thus highlighting the generalizability of the findings and their potential to open new possibilities in the design of molecular catalysts.

Enhanced Four-Electron Selective Oxygen Reduction Reaction at Carbon-Nanotube-Supported Sulfonic-Acid-Functionalized Copper Phthalocyanine

In the present work, the oxygen reduction reaction (ORR) is explored in an acidic medium with two different catalytic supports (multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped multi-walled carbon nanotubes (NMWCNTs)) and two different catalysts (copper phthalocyanine (CuPc) and sulfonic acid functionalized CuPc (CuPc-SO3 - )). The composite, NMWCNTs-CuPc-SO3 - exhibits high ORR activity (assessed based on the onset potential (0.57 V vs. reversible hydrogen electrode) and Tafel slope) in comparison to the other composites. Rotating ring disc electrode (RRDE) studies demonstrate a highly selective four-electron ORR (less than 2.5 % H2 O2 formation) at the NMWCNTs-CuPc-SO3 - . The synergistic effect of the catalyst support (NMWCNTs) and sulfonic acid functionalization of the catalyst (in CuPc-SO3 - ) increase the efficiency and selectivity of the ORR at the NMWCNTs-CuPc-SO3 - . The catalyst activity of NMWCNTs-CuPc-SO3 - has been compared with many reported materials and found to be better than several catalysts. NMWCNTs-CuPc-SO3 - shows high tolerance for methanol and very small deviation in the onset potential (10 mV) between the linear sweep voltammetry responses recorded before and after 3000 cyclic voltammetry cycles, demonstrating exceptional durability. The high durability is attributed to the stabilization of CuPc-SO3 - by the additional coordination with nitrogen (Cu-Nx ) present on the surface of NMWCNTs.

Ultrafast fabrication of robust electrocatalyst having Fe/Fe3C and CuNC for enhanced oxygen reduction reaction activity

The search for ultrafast and simple methods to fabricate non-noble metal catalysts to boost electrocatalytic oxygen reduction reaction (ORR) is still ongoing. Herein, we demonstrate a one-step microwave-assisted heating method to prepare copper nitride/iron/iron carbide nanoparticle hybrids (CuNC/Fe/Fe₃C/CNT). This ultrafast heating method induces plentiful carbon-wrapped metal and Fe₃C nanoparticles that are attached to the surface of CNT and scattered nanosheets. The CuNC/Fe/Fe₃C/CNT exhibit a half-wave potential (E_1/2) of 0.886 V toward the ORR in alkaline solution, with 220 mV more positive E_1/2 than that of CuNC/CNT and Fe/Fe₃C/CNT respectively. The activity of as-prepared catalysts is discussed by investigating their structures and compositions and their relationship with the ORR performance. Detailed analysis results disclose that the high activity of the CuNC/Fe/Fe₃C/CNT catalysts could be attributed to the interaction of CuNC and Fe/Fe₃C species. To be specific, as the electron donor, Fe/Fe₃C nanoparticles induce electron localization and promote the formation of Cu (δ + )-NC (0 < δ < 2), therefore leading to the improvement of the ORR performance. This work may offer an ultrafast way to construct efficient catalysts with enhanced ORR performance.

The joint effect of electrical conductivity and surface oxygen functionalities of carbon supports on the oxygen reduction reaction studied over bare supports and Mn–Co spinel/carbon catalysts in alkaline media

Mn–Co spinel/carbon electrocatalyst performance exhibits a volcano-type shape which results from a trade-off between electrical conductivity and the amount of oxygen groups.

Carbon-Based Electrocatalysts Derived From Biomass for Oxygen Reduction Reaction: A Minireview

Oxygen reduction reaction (ORR) electrocatalysts derived from biomass have become one of the research focuses in hetero-catalysis due to their low cost, high performance, and reproducibility properties. Related researches are of great significance for the development of next-generation fuel cells and metal-air batteries. Herein, the preparation methods of various biomass-derived catalysts and their performance in alkaline, neutral, and acidic media are summarized. This review clarifies the research progress of biomass carbon-based electrocatalysts for ORR in acidic, alkaline and neutral media, and discusses the future development trends. This minireview can give us an important enlightenment to practical application in the future.

Catalytic performance of graphene quantum dot supported manganese phthalocyanine for efficient oxygen reduction: density functional theory approach

The thermodynamic free-energy diagrams predict that MnPc/GQD is more active toward ORR than the isolated MnPc, clearly highlighting the effect of the GQD matrix on ORR activity from a thermodynamic perspective.

Nitrogen/sulfur dual-doped reduced graphene oxide supported CuFeS2 as an efficient electrocatalyst for the oxygen reduction reaction

At present, low-cost and efficient electrocatalysts for accelerating the oxygen reduction reaction in fuel cells are highly desired.