W-doping induced abundant active sites in a 3D NiS2/MoO2 heterostructure as an efficient electrocatalyst for urea oxidation and hydrogen evolution reaction

Developing efficient and robust non-precious-metal-based catalysts to accelerate electrocatalytic reaction kinetics is crucial for electrochemical water-urea splitting. Herein, Fe-doped NiS-NiS2 heterostructured microspheres, an electrocatalyst, are synthesized via etching Prussian blue analogues following a controlled annealing treatment. The resulting microspheres are constructed by mesoporous nanoplates, granting the virtues of large surface areas, high structural void porosity, and accessible inner surface. These advantages not only provide more redox reaction centers but also strengthen structural robustness and effectively facilitate the mass diffusion and charge transport. Density functional theory simulations validate that the Fe-doping improves the conductivity of nickel sulfides, whereas the NiS-NiS2 heterojunctions induce interface charge rearrangement for optimizing the adsorption free energy of intermediates, resulting in a low overpotential and high electrocatalytic activity. Specifically, an ultralow overpotential of 270 mV at 50 mA cm-2 for the oxygen evolution reaction (OER) is achieved. After adding 0.33 M urea into 1 M KOH, Fe-doped NiS-NiS2 obtains a strikingly reduced urea oxidation reaction potential of 1.36 V to reach 50 mA cm-2 , around 140 mV less than OER. This work provides insights into the synergistic modulation of electrocatalytic activity of non-noble catalysts for applications in energy conversion systems.

Construction of Fe-doped NiS-NiS2 Heterostructured Microspheres Via Etching Prussian Blue Analogues for Efficient Water-Urea Splitting.

Urea electrooxidation has received considerable attention because of its tremendous practical application in environmental protection and energy regeneration. As an electrochemical reaction, the catalytic performance of urea oxidation is highly...

A review of hetero-structured Ni-based active catalysts for urea electrolysis

The thermal field effect effectively boosts water splitting electrocatalysis by lowering activation energy barriers and accelerating sluggish kinetics. Solar-powered light-to-heat conversion of photothermal materials enabling desirable surface heat localization satisfies the integration of in situ heating to supply an additional energy source to promote electrocatalytic reactions. Based on these concepts, we herein report a robust photothermal–electrocatalytic water splitting system based on broadband solar harvesting nickel phosphide (Ni2P) within a heat-insulating quasi-Ni-BDC-MOF. Benefiting from the controllable thermal treatment for partial deligandation and synchronous phosphorization, the highly dispersed ultrafine Ni2P nanoparticles are spatially confined within quasi-Ni-BDC-MOF nanosheets, ensuring the effective utilization of local heat assisted by heat-insulating quasi-Ni-BDC-MOF to suppress heat loss. The resulting black Ni2P@quasi-Ni-BDC exhibits an ultrasensitive and stable light-to-heat response under simulated solar light illumination. By coupling with this excellent photothermal performance, Ni2P@quasi-Ni-BDC under full spectrum light illumination demonstrates the ultralow overpotentials of 246 and 218 mV to deliver 100 mA cm−2 current density for oxygen and hydrogen evolution reactions and shows negligible degradation over operating for 50 h and excellent recyclability under several repeated on–off cycles. This performance compares favorably with those of previously reported electrocatalysts working at large currents and outperforms those of most of the photothermal electrocatalysts for water splitting.

Photothermally boosted water splitting electrocatalysis by broadband solar harvesting nickel phosphide within a quasi-MOF

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.

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

Urea oxidation reaction (UOR) has been proposed to replace the formidable oxygen evolution reaction (OER) to reduce the energy consumption for producing hydrogen from electrolysis of water owing to its much lower thermodynamic oxidation potential compared to that of the OER. Therefore, exploring a highly efficient and stable hydrogen evolution and urea electrooxidation bifunctional catalyst is the key to achieve economical and efficient hydrogen production. In this paper, we report a heterostructured sulfide/phosphide catalyst (Ni3S2-Ni3P/NF) synthesized via one-step thermal treatment of Ni(OH)2/NF, which allows the simultaneous occurrence of phosphorization and sulfuration. The obtained Ni3S2-Ni3P/NF catalyst shows a sheet structure with an average sheet thickness of ∼100 nm, and this sheet is composed of interconnected Ni3S2 and Ni3P nanoparticles (∼20 nm), between which there are a large number of accessible interfaces of Ni3S2-Ni3P. Thus, the Ni3S2-Ni3P/NF exhibits superior performance for both UOR and hydrogen evolution reaction (HER). For the overall urea-water electrolysis, to achieve current densities of 10 and 100 mA cm-2, cell voltage of only 1.43 and 1.65 V is required using this catalyst as both the anode and the cathode. Moreover, this catalyst also maintains fairly excellent stability after a long-term testing, indicating its potential for efficient and energy-saving hydrogen production. The theoretical calculation results show that the Ni atoms at the interface are the most efficient catalytically active site for the HER, and the free energy of hydrogen adsorption is closest to thermal neutrality, which is only 0.16 eV. A self-driven electron transfer at the interface, making the Ni3S2 sides become electron donating while Ni3P sides become electron withdrawing, may be the reason for the enhancement of the UOR activity. Therefore, this work shows an easy treatment for enhancing the catalytic activity of Ni-based materials to achieve high-efficiency urea-water electrolysis.

Heterostructured Ni 3 S 2 -Ni 3 P/NF as a Bifunctional Catalyst for Overall Urea-Water Electrolysis for Hydrogen Generation.

Hetero-structured V-Ni3S2@NiOOH core-shell nanorods from an electrochemical anodization for water splitting

Ordered Mesoporous Carbon Confined Highly Dispersed PtCo Alloy for the Oxygen Reduction Reaction: The Effect of Structure and Composition on Performance

Jinchao Liu

Papers

Heterostructured Ni 3 S 2 -Ni 3 P/NF as a Bifunctional Catalyst for Overall Urea-Water Electrolysis for Hydrogen Generation.

Hetero-structured V-Ni3S2@NiOOH core-shell nanorods from an electrochemical anodization for water splitting

Ordered Mesoporous Carbon Confined Highly Dispersed PtCo Alloy for the Oxygen Reduction Reaction: The Effect of Structure and Composition on Performance