Co3O4 Nanosheet Arrays on Ni Foam as Electrocatalyst for Oxygen Evolution Reaction

Optimizing charge pathways by interface engineering in Fe2O3/Co3O4/Co(PO3)2 heterostructures for superior oxygen evolution reaction

The Oxygen Evolution Reaction (OER) is vital for energy conversion and storage. This study presents a multi-heterostructure catalyst, Fe2O3/Co3O4/Co(PO3)2, created by encapsulating Fe ions in COF/MOF pores through grinding and one-step pyrolysis. The catalyst demonstrates exceptional OER performance, achieving an ultra-low overpotential of 232 mV, outperforming the Co3O4/Co(PO3)2 single heterostructure. The unique design significantly reduces electron transfer resistance (Rct = 5.88 Ω), enhancing electron transfer efficiency at the heterojunction interface. Additionally, the catalyst's increased specific surface area and mesoporosity boost the number of active catalytic sites. Density functional theory (DFT) studies reveal that optimized geometric structures and altered electron density around Co and Fe sites shift the d-band center, facilitating electron migration and improving adsorption and desorption processes. This research provides novel insights into creating high-efficiency OER electrocatalysts with heterogeneous interfaces, advancing sustainable energy technologies.

Nanoparticles of Mixed-Valence Oxides MnXCO3-XO4 (0 ≤ X ≤ 1) Obtained with Agar-Agar from Red Algae (Rhodophyta) for Oxygen Evolution Reaction

The development of efficient electrocatalysts for the oxygen evolution reaction (OER) is of paramount importance in sustainable water-splitting technology for hydrogen production. In this context, this work reports mixed-valence oxide samples of the Mn_XCo_3-XO₄ type (0 ≤ X ≤ 1) synthesized for the first time by the proteic sol-gel method using Agar-Agar as a polymerizing agent. The powders were calcined at 1173 K, characterized by FESEM, XRD, RAMAN, UV-Vis, FT-IR, VSM, and XPS analyses, and were investigated as electrocatalysts for the oxygen evolution reaction (OER). Through XRD analysis, it was observed that the pure cubic phase was obtained for all samples. The presence of Co³⁺, Co²⁺, Mn²⁺, Mn³⁺, and Mn⁴⁺ was confirmed by X-ray spectroscopy (XPS). Regarding the magnetic measurements, a paramagnetic behavior at 300 K was observed for all samples. As far as OER is concerned, it was investigated in an alkaline medium, where the best overpotential of 299 mV vs. RHE was observed for the sample (MnCo₂O₄), which is a lower value than those of noble metal electrocatalysts in the literature, together with a Tafel slope of 52 mV dec^-1, and excellent electrochemical stability for 15 h. Therefore, the green synthesis method presented in this work showed great potential for obtaining electrocatalysts used in the oxygen evolution reaction for water splitting.

Trimetallic MOF-74 Films Grown on Ni Foam as Bifunctional Electrocatalysts for Overall Water Splitting

Developing earth-abundant and high-performance electrocatalysts for water splitting has long been a vital research in energy conversion field. Herein, we report the preparation of a series of trimetallic uniform Mn_x Fe_y Ni-MOF-74 films in-situ grown on nickel foam, which can be utilized as bifunctional electrocatalysts towards overall water splitting in alkaline media. The introduction of Mn can simultaneously regulate the morphology of MOF-74 to form uniform film and modulate electronic structure of Fe to form more Fe(II)-O-Fe(III) motifs, which is conducive to the exposure of active sites and stabilizing high-valent metal sites. The optimized Mn_0.52 Fe_0.71 Ni-MOF-74 film electrode showed excellent electrocatalytic performance, affording a current density of 10 mA ⋅ cm^-2 at an overpotential of 99 mV for HER and 100 mA ⋅ cm^-2 at an overpotential of 267 mV for OER, respectively. Assembled as an electrolyser, Mn_0.52 Fe_0.71 Ni-MOF-74 film electrode exhibited excellent performance towards overall water splitting, with ultralow overpotential of 245 and 462 mV to achieve current density of 10 and 100 mA ⋅ cm^-2 , respectively. This work provides a new view to develop multi-metal MOF-based electrocatalysts.

A Co3O4/MnCO3 heterojunction on three-dimensional nickel foam for an enhanced oxygen evolution reaction

A Co₃O₄/MnCO₃ heterojunction on NF with a unique architecture exhibits prominent OER activity and stability that is superior to most Co₃O₄-based catalysts.