Porphyrinic Metal-Organic Framework-Templated Fe-Ni-P/Reduced Graphene Oxide for Efficient Electrocatalytic Oxygen Evolution

π-Conjugated Molecule Boosts Metal-Organic Frameworks as Efficient Oxygen Evolution Reaction Catalysts

To improve the efficiency of water electrolysis, developing efficient oxygen evolution reaction (OER) electrocatalysis is extremely important due to its four-electron transfer dynamics. In this work, a π-conjugated molecule (2,3,6,7,10,11-hexahydroxytriphenylene, HHTP), which can accelerate the electron transfer, is coated directly on pristine ZIF-67, resulting in a composite named HHTP@ZIF-67, via a simple one-step solvothermal method. The obtained HHTP@ZIF-67 possesses a Brunauer-Emmett-Teller surface area of 2013.9 m² g^-1 and displays microporous behavior, which can provide enough active sites for OER. The double-layer capacitance of HHTP@ZIF-67 is also enhanced, corresponding to an enlarged electrochemical active surface area. HHTP@ZIF-67 presents a quite low overpotential of 238 mV at 10 mA cm^-2 in 1.0 m KOH. This material synthesized via the simple coating strategy is promising in the application of energy conversion devices.

A Co2 P/WC Nano-Heterojunction Covered with N-Doped Carbon as Highly Efficient Electrocatalyst for Hydrogen Evolution Reaction

The hydrogen evolution reaction (HER) produces clean hydrogen through an electrochemical process. However, new nonprecious-metal electrocatalysts for the HER are required to reduce the consumption of energy. Herein, we report a new Co₂ P/WC nano-heterojunction that consists of Co₂ P and WC composite phases coated with a few-layer N-doped graphitic carbon shells (Co₂ P/WC@NC). The composite was prepared by a one-step annealing of the polyoxometalate Na₉ (NH₄ )₅ [{(B-α-PW₉ O₃₄ )Co₃ (OH)(H₂ O)₂ (Ale)}₂ Co]⋅35 H₂ O (Co₇ P₆ W₁₈ ) and dicyandiamide (DCA). The preparation method consisted of the simultaneous phosphorization of Co and carbonization of W in a confined space to isolate a Co₂ P/WC nano-heterojunction phase for the first time. Co₂ P/WC@NC facilitated the generation of hydrogen in the electrolysis process, which had an overpotential of only 91 mV at a current density of 10 mA cm^-2 in the acid solution; an excellent HER performance (2 H⁺ +2 e^- →H₂ ) and Tafel slope (40 mV dec^-1 ) as well as durability over a period of 50 h were achieved. Theoretical calculations showed that the Co₂ P, WC, and N_pyridinic C dopants in the material synergistically promoted the HER activity rather than the individual constituents. Furthermore, Co₂ P/WC@NC nano-heterojunctions showed good HER performance in the whole pH range of electrolytes and considerable durability in acidic media containing transition metal ions, which may attract more attention for the exploration and optimization of nano-heterojunction catalysts for the HER.

Self-Template Synthesis of Co-Se-S-O Hierarchical Nanotubes as Efficient Electrocatalysts for Oxygen Evolution under Alkaline and Neutral Conditions

We develop a facile self-template synthetic method to construct hierarchical Co-Se-S-O (CoSe _xS_{2- x}@Co(OH)₂) nanotubes on a carbon cloth as a self-standing electrode for electrocatalytic oxygen evolution reaction (OER). In the synthetic process, separate selenization and sulfurization on the Co(OH)F precursor in different solvents have played an important role in constructing CoSe _xS_{2- x} (Co-Se-S) hierarchical nanotubes, which was further transformed into the nanotube-like Co-Se-S-O via an in situ electrochemical oxidation process. The Co-Se-S-O obtained by the Kirkendall effect through two stepwise anion-exchange reactions represents the first quaternary Co-Se-S-O nanotube array, which dramatically enhances its surface area and conductivity. Further, it only requires low overpotentials of 230 and 480 mV to achieve a 10 mA cm^-2 current density. The OER performance of Co-Se-S-O is much more efficient than that of its monochalcogenide counterparts, as well as the commercial benchmark catalyst IrO₂.

Simple preparation of carbon–bimetal oxide nanospinels for high-performance bifunctional oxygen electrocatalysts

Carbon–bimetal oxide nanospinels synthesized by a single step of autocombustion show high activity for oxygen evolution and reduction.

Dual-Functional Electrocatalyst Derived from Iron-Porphyrin-Encapsulated Metal-Organic Frameworks

Active, stable electrocatalysts based on non-precious metals for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are critical for the development of cost-effective, efficient renewable energy technologies. Here, Fe/Fe₃C-embedded nitrogen-doped carbon was fabricated via pyrolysis of iron-porphyrin-encapsulated mesoporous metal-organic frameworks [PCN-333 (Fe), where "PCN" stands for "porous coordination network"] at 700 °C. The various characterization techniques confirmed that Fe- and Fe₃C-containing Fe-N-C material (FeP-P333-700) was successfully prepared by pyrolysis of porphyrin-encapsulated PCN-333 (Fe). FeP-P333-700 exhibited superior electrocatalytic performance for the ORR and HER owing to the synergistic effect of Fe/Fe₃C and Fe-N-C active sites.