Co(OH) 2 Nanosheets Array Doped by Cu 2+ Ions with Optimal Electronic Structure for Urea‐Assisted Electrolytic Hydrogen Generation

In Situ Assembly of a Superaerophobic CoMn/CuNiP Heterostructure as a Trifunctional Electrocatalyst for Ampere-Level Current Density Urea-Assisted Hydrogen Production

Urea electrolysis is a promising energy-efficient hydrogen production process with environmental benefits, but the lack of efficient and sustainable ampere-level current density electrocatalysts fabricated through simple methods is a major challenge for commercialization. Herein, we present an efficient and stable heterostructure electrocatalyst for full urea and water electrolysis in a convenient and time-efficient preparation manner. Overall, superhydrophilic/superaerophobic CoMn/CuNiP/NF exhibits exceptional performance for the hydrogen evolution reaction (HER) (-33.8, -184.4, and -234.8 mV at -10, -500, and -1000 mA cm-2, respectively), urea electro-oxidation reaction (UOR) [1.28, 1.43, and 1.51 V (vs RHE) at 10, 500, and 1000 mA cm-2, respectively], and oxygen evolution reaction (OER) [1.45, 1.67, and 1.74 V (vs RHE) at 10, 500, and 1000 mA cm-2, respectively]. Moreover, the superaerophobic CoMn/CuNiP/NF demonstrates promising potential in full urea (1.33, 1.57, and 1.60 V at 10, 500, and 1000 mA cm-2, respectively) and water (1.46 V, 1.78, and 1.86 at 10, 500, and 1000 mA cm-2, respectively) electrolysis. Based on X-ray photoelectron spectroscopy results, it was determined that the surface of the CoMn/CuNiP electrode was rich in redox pairs such as Ni2+/Ni3+, Cu+/Cu2+, Co2+/Co3+, and Mn2+/Mn3+, which are crucial for the formation of active sites for the OER and UOR, such as NiOOH, MnOOH, and CoOOH, thereby enhancing the catalytic activity. Besides, the in situ assembled CoMn/CuNiP/NF displayed highly stable performance for HER, OER, and UOR with high Faradaic efficiency for over 500 h. This research offers a simple and efficient method for manufacturing a high-efficiency and stable trifunctional electrocatalyst capable of delivering ampere-level current density in urea-assisted hydrogen production. Our density functional theory calculations reveal the potential of CoMn/CuNiP as an effective catalyst, enhancing the electronic properties and catalytic performance. The near-zero Gibbs free-energy change for HER underscores its promise, while reduced CO2 desorption energies and charge redistribution support efficient UOR. These findings signify CoMn/CuNiP's potential for electrochemical applications.

High-Entropy Oxide Derived from Metal-Organic Framework as a Bifunctional Electrocatalyst for Efficient Urea Oxidation and Oxygen Evolution Reactions

High-entropy oxides (HEOs) offer unique features through a combination of incompatible metal cations to a single crystalline lattice. Owing to their special characteristics such as abundant cation compositions, high entropy stabilization, chemical and thermal stability, and lattice distortion effect, they have drawn ever-increasing attention for various applications. However, very few studies have been reported for catalytic application, and developing HEOs with large surface areas for efficient catalytic application is still in infancy. Herein, we design nanostructured HEO of (FeNiCoCrCu)₃O₄ using metal-organic frameworks (MOFs) as sacrificial templates to achieve a large surface area, high density of exposed active sites, and more oxygen vacancies. Single-crystalline phase HEOs with surface area as large as 206 m² g^-1 are produced and further applied as bifunctional electrocatalysts for the urea oxidation reaction (UOR) and oxygen evolution reaction (OER). Benefiting from enhanced oxygen vacancies and a large surface area with abundant exposed active sites, the optimized HEO exhibited excellent electrocatalytic activity toward UOR with a very low potential of 1.35 V at the current density of 10 mA cm^-2 and showed long-term stability for 36 h operation, making a significant catalytic performance over previously reported HEOs. Moreover, the HEO demonstrated an efficient catalytic performance toward OER with a low overpotential of 270 mV at 10 mA cm^-2 and low Tafel slope of 49 mV dec^-1. The excellent catalytic activity is ascribed to the starting MOF precursor and favorable high-entropy effect.

Ir-doped Co(OH)2 Nanosheets as Efficient Electrocatalyst for Oxygen Evolution Reaction

In recent years, Co-based metal-organic frameworks (Co-MOFs) have received significant research interest because of their large specific surface area, high porosity, tunable structure and topological flexibility. However, the comparatively weak...