Electroactive Edge‐Site‐Enriched α‐Co 0.9 Fe 0.1 (OH) x Nanoplates for Efficient Overall Water Splitting

Se vacancies and interface engineering modulated bifunctionality prussian blue analogue derivatives for overall water splitting

It is a challenging task to design and synthesize stable, and high-performance non-precious metals bifunctional catalysts for water-splitting. Herein, the coupling between Se vacancy and interface engineering is highlighted to synthesize a unique CoFeSe hollow nanocubes structure on MXene-modified nickel foam (NF) by in-situ phase transition from bifunctionality prussian blue analogue (PBA) derivatives (VSe-CoFeSe@MXene/NF). DFT theory reveals that the Se vacancy and interface engineering modulate the surface electronic structure and optimize the surface adsorption energy of the intermediates. Experimental data also confirm that the as-prepared CoFeSe@MF catalyst exhibits advanced electrocatalytic properties, 283 mV (OER) and 67 mV (HER) are required to drive the current density of 10 mA cm-2. Notably, it is assembled into a two-electrode system for integral water decomposition, which only requires a low cell potential of 1.57 V at current of 10 mA cm-2, together with excellent durability for 48 h. The strategy is expected to provide a new direction for the design and construction of highly efficient collaborative integrated water decomposition electrocatalysts.

Impact of Iron in Three-Dimensional Co-MOF for Electrocatalytic Water Oxidation

The integration of iron (Fe) into a cobalt metal-organic framework (Co-MOF) tunes the electronic structure of the parent MOF as well as enhances their electrocatalytic characteristics. By using pyrazine and hydrofluoric acid, we have synthesized three-dimensional Co-MOF [CoFC₄H₄N₂(SO₄)_0.5], (1), and Fe-MOF [FeFC₄H₄N₂(SO₄)_0.5], (2), through a single-step solvothermal method. Further, a series of bimetallic (having both Co and Fe metal centers) MOFs [Co_1-xFe_xFC₄H₄N₂(SO₄)_0.5] were synthesized with variable concentrations of Fe, and their electrocatalytic performances were analyzed. The optimized amount of Fe significantly impacted the electrocatalytic behavior of the bimetallic MOF toward water oxidation. Particularly, the Co_0.75Fe_0.25-MOF needs only 239 and 257 mV of overpotential to deliver 10 and 50 mA/cm² current density, respectively, in alkaline electrolytic conditions. The Co_0.75Fe_0.25-MOF shows a lower Tafel slope (42 mV/dec.) among other bimetallic MOFs and even the commercial RuO₂, and it has excellent durability (with ∼8 mV increases in overpotential after 18 h of electrolysis) and 97.05% Faradaic efficiency, which further evident its catalytic excellency. These findings explore the intrinsic properties of MOF-based electrocatalysts and prospect the suitability for future water electrolysis.

Facile Synthesis of 3d Transition-Metal-Doped α-Co(OH)2 Nanomaterials in Water-Methanol Mediated with Ammonia for Oxygen Evolution Reaction

Layered cobalt hydroxides are cost-efficient electrocatalysts for oxygen evolution reaction (OER) in the field of energy conversion. Herein, we developed a facile synthesis method of 3d transition-metal-doped α-Co(OH)₂ nanomaterials mediated with ammonia in water-methanol at room temperature. The doping of Cu²⁺ and Ni²⁺ leads to flower-like nanostructures similar to pure α-Co(OH)₂, whereas the doping of Fe²⁺ produces nanoparticles with more than 2 times larger surface area in comparison with the Cu²⁺- and Ni²⁺-doped nanoflowers. The obtained dispersion with the addition of Nafion can be used directly as an electrocatalyst for OER with excellent catalytic activity, especially that the overpotential of Fe²⁺ doped is as low as 290 mV at 10 mA cm^-2 and the turnover frequency is improved by 3 times as compared with that of α-Co(OH)₂. Furthermore, the catalyst can be loaded onto foam nickel, which presents excellent durability with the current density unchanged under continuous chronoamperometry reaction for as long as 12 h and almost quantitative faradaic efficiency. The superior electrocatalytic properties combined with the simple synthesis without the tedious purification procedure is very promising for OER.