Enhancing One-Dimensional Charge Transport in Metal-organic Framework Hexagonal Nanorods for Electrocatalytic Oxygen Evolution

Electronic Buffering Mechanism Enhances Stability and Water Oxidation Efficiency of CeO2@NiFe-LDH

Nickel-iron layered double hydroxide shows significant promise as an electrocatalyst in facilitating oxygen evolution reactions. But its development is hindered by low conductivity and insufficient cycling stability. Herein, the synthesis of a hierarchically structured heterostructure catalyst, CeO2@NiFe LDH, is reported through a straightforward two-step process involving hydrothermal treatment. The catalyst realizes a significant breakthrough in OER catalytic performance and stability. At a current density of 100 mA cm-2, the overpotentials amount to 255 mV in 1 M KOH, 263 mV in simulated seawater with alkaline conditions, and 346 mV in actual alkaline seawater. After 200 hours of continuous operation under high current density in simulated alkaline seawater, the morphology with no significant alterations observed, highlighting its high stability in complex seawater environments. Introducing CeO2 optimizes the binding energy of the OH intermediate, which facilitates the formation and dissociation of the OOH intermediate. In situ Raman analysis demonstrates the positive impact of CeO2 on the generation of active species. This research emphasizes the efficacy of CeO2 in improving the performance and durability of NiFe LDH for oxygen evolution reactions.

Robust High-performance Bifunctional Porous Cobalt MOF-Based Catalysts for Overall Water Splitting

MOF-based materials, as bifunctional catalysts for electrocatalytic water splitting, play an important role in the application and development of clean fuel hydrogen energy. This study presents a series of novel 3D Co-based MOFs with layered networks, including [Co(4,4'-bipy)0.5(aip)(CH3OH)·H2O]n (Co-MOF 1), [Co2(1,3'-bit)(aip)2(CH3OH)·H2O]n (Co-MOF 2), [Co(4,4'-bipb)(aip)]n (Co-MOF 3), and [Co2(4,4'-bipe)(aip)2·1.5H2O]n (Co-MOF 4). Their single-crystal structures of Co-MOFs 1-4 are characterized and analyzed before being applied in alkaline solutions for water decomposition (OER and HER). The electrocatalytic tests indicate that Co-MOFs 1-4 exhibit a good performance. Notably, Co-MOF 4 exhibits great behavior which has low overpotentials of 94 and 188 mV (OER) as well as 185 and 352 mV (HER) at the currents of 10 and 100 mA cm-2, respectively. In comparison with Co-MOFs 1-3, Co-MOF 4 has the lowest Tafel slopes, highest ECSA, and smallest resistance. The immanent qualities, such as distinct interwoven long chain layered structure, unsaturated coordination modes, and synergistic catalytic qualities among Co ions, contribute to explaining the results. The fundamentals provide valuable information for the investigation of innovative MOF-based bifunctional electrocatalysts for overall water splitting.

Borate Anion Dopant Inducing Oxygen Vacancies over Co3O4 Nanocages for Enhanced Oxygen Evolution

The rational design of cost effective and highly efficient oxygen evolution reaction (OER) catalysts plays an extremely important role in promoting the commercial applications of electrochemical water splitting. Herein we reported a sacrificial template strategy for the preparation of borate anion doped Co3O4@ZIF-67 nanocages assembled with nanosheets (B-Co3O4@ZIF-67) by hydrothermal boronation of zeolitic imidazolate framework-67 (ZIF-67). During the preparation process, two different kinds of borate anion sources were found to regulate the morphological structures by tuning the etching rate between ZIF precursors and the borate anion. Moreover, borate anion doping was also found to induce oxygen vacancy defects, which is beneficial for modulating the electronic structure and accelerating electron transport. Meanwhile, the resultant B-Co3O4@ZIF-67 nanocages possess a large specific surface area, which is beneficial for the mass transfer of the electrolyte and exposing more catalytic active sites. Benefiting from the advantages above, the resultant B-Co3O4@ZIF-67 nanocages exhibit impressive OER performance with a small overpotential of 334 mV, a current density of 10 mA cm−2, a small Tafel slope of 73.88 mV dec−1, as well as long-term durability in an alkaline electrolyte.