Lanthanum-incorporated β-Ni(OH)2 nanoarrays for robust urea electro-oxidation

NiCr-LDH/V4C3 MXene nanocomposites as an efficient electrocatalyst for urea oxidation

The quest for highly efficient electrocatalysts for direct urea fuel cells (DUFCs) is vital in addressing the energy deficits and environmental crisis. Ni-based LDHs are widely known for their substantial capability in urea oxidation reactions (UOR). This study involved the synthesis of NiCr-LDH/V4C3 MXene nanocomposites (NCVs) and the evaluation of their electrochemical efficiency towards UOR. The hybridization of V4C3 with NiCr-LDH improved the redox kinetics of the nanocomposite. NCV-21 achieved a notable efficiency of 10 mA cm-2 at a lower onset potential of 1.36 V versus the reversible hydrogen electrode in a 1.0 M KOH solution containing 0.33 M urea. Furthermore, it demonstrated an enhanced current density of 112.64 mA cm-2 and long-term durability. The robust interaction and electronic coupling between NiCr-LDH and V4C3 MXene, marked by superior current density and significant charge transfer, confers the nanocomposite with remarkable catalytic activity and stability towards substantial urea oxidation performance. Based on the results obtained, the NiCr-LDH/V4C3 MXene nanocomposite is an efficient anodic catalyst for urea oxidation. This study will open a new avenue for the development of various LDH/MXene nanocomposites for energy conservation applications.

Charge-redistributed Co3O4/Fe0.3Co0.7P heterointerfaces for efficient electrocatalytic urea oxidation

Charge-redistributed Co3O4/Fe0.3Co0.7P heterointerfaces are designed for effective electrocatalytic urea oxidation in alkaline medium, delivering excellent performance with only 1.41 V vs. RHE at 100 mA cm-2, low Tafel slope of 74 mV dec-1 and 36-h robust stability. The fine regulation of charge redistribution through heterointerfaces provides an effective strategy to design highly efficient electrocatalysts.

Ceria-Graphene Oxide Nanocomposite for Electro-oxidation of Urea: An Experimental and Theoretical Investigation

This study explores the potential of ceria-graphene oxide (CeO2-GO) nanocomposites as efficient electrocatalysts for urea electro-oxidation (UOR). This work combines experimental and theoretical investigations and characterization techniques confirm the successful formation of the CeO2 embedded on graphene oxide sheets. UOR activity was found to be dependent on both OH- and urea concentrations. The optimal UOR performance was achieved in a 0.1 M urea and 1.0 M KOH solution, as evidenced by the low Tafel slope of 60 mV/dec and high turnover frequency (TOF) of 1.690 s-1. DFT calculations revealed that the CeO2-GO nanocomposite exhibited strong urea adsorption due to its favorable bond lengths (Ce-O: 2.58 Å, O-H: 1.77 Å) and high adsorption energy (-1.05 eV). These findings revealed that the CeO2-GO nanocomposites are promising as efficient and durable electrocatalysts for urea conversion to valuable products like nitrogen and hydrogen gas, with potential applications in clean energy generation and ammonia synthesis.

Engineering advanced noble-metal-free electrocatalysts for energy-saving hydrogen production from alkaline water via urea electrolysis

When the anodic oxygen evolution reaction (OER) of water splitting is replaced by the urea oxidation reaction (UOR), the electrolyzer can fulfill hydrogen generation in an energy-economic manner for urea electrolysis as well as sewage purification. However, owing to the sluggish kinetics from a six-electron process for UOR, it is in great demand to design and fabricate high-performance and affordable electrocatalysts. Over the past years, numerous non-precious materials (especially nickel-involved samples) have offered huge potential as catalysts for urea electrolysis under alkaline conditions, even in comparison with frequently used noble-metal ones. In this review, recent efforts and progress in these high-efficiency noble-metal-free electrocatalysts are comprehensively summarized. The fundamentals and principles of UOR are first described, followed by highlighting UOR mechanism progress, and then some discussion about density functional theory (DFT) calculations and operando investigations is given to disclose the real reaction mechanism. Afterward, aiming to improve or optimize UOR electrocatalytic properties, various noble-metal-free catalytic materials are introduced in detail and classified into different classes, highlighting the underlying activity-structure relationships. Furthermore, new design trends are also discussed, including targetedly designing nanostructured materials, manipulating anodic products, combining theory and in situ experiments, and constructing bifunctional catalysts. Ultimately, we point out the outlook and explore the possible future opportunities by analyzing the remaining challenges in this booming field.

Water activating fresh NiMo foam for enhanced urea electrolysis

Recently, production of hydrogen (H2) through the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) has acquired great attention because it is more environmentally friendly and energy-saving. Herein, an approach of water activation was developed for in situ growth of NiMo LDH nanosheet arrays on NiMo foam without using any binder or pressurizing or heating steps. The obtained NiMo foam electrodes showed exceptional catalytic activity and durability for both the UOR and HER. This work offers a new standpoint on designing electrodes with high activation for efficient and sustainable hydrogen production coupled with urea organic oxidation.

Metal organic framework-assisted in-situ synthesis of β-NiMnOOH nanosheets with abundant NiOOH active sites for efficient electro-oxidation of urea

NiOOH has been considered as the active center for urea oxidation reaction (UOR), but it remains challenging to synthesize high-performance NiOOH-based catalysts. Herein, we realize the synthesis of a high-performance NiOOH-based catalyst through in-situ transformation from the NiMn-based metal-organic framework to NiMnOOH. X-ray photoelectron spectroscopy characterization shows that the Ni3+/Ni2+ ratio in the NiMnOOH is 3.9 times as big as that in the Ni(OH)2, and in-situ Raman characterization further consolidates the presence of the NiOOH species in the NiMnOOH and as well unveils the faciliated Ni2+/Ni3+ redox reaction. The abundant NiOOH species, the markedly facilitated Ni2+/Ni3+ redox reaction and the Ni-Mn synergy contribute to the high intrinsic activity of the NiMnOOH towards UOR. The NiMnOOH exhibits an impressively low onset potential of 1.305 V vs reversible hydrogen electrode (RHE) and requires only a small potential of 1.34 V vs RHE to deliver a current density of 100 mA cm-2 in 1.0 M KOH + 0.33 M urea. In addition, the NiMnOOH catalyst possesses good long-term working stability.

In situ construction of Fe3O4@FeOOH for efficient electrocatalytic urea oxidation

Substituting water oxidation half of water splitting with anodic oxidation of urea can reduce the cost of H₂ production and provide an avenue for treating urea-rich wastewater. However, developing an efficient and stable electrocatalyst is necessary to overcome the indolent kinetics of the urea oxidation reaction (UOR). Accordingly, we have used the Schikorr reaction to deposit Fe₃O₄ particles on the nickel foam (Fe₃O₄/NF). Results from the various analysis indicated that under the operational conditions, Fe₃O₄ underwent surface reconstruction to produce a heterolayered structure wherein a catalytically active FeOOH layer encased a conducting Fe₃O₄. Fe₃O₄/NF outperformed RuO₂ as a UOR catalyst and delivered a current density of 10 50 and 100 mA cm^-2 at low applied potentials of 1.38 1.42 and 1.46 V, respectively, with a Tafel slope of 28 mV dec^-1. At the applied potential of 1.4 V, Fe₃O₄/NF demonstrated a turnover frequency (TOF) of 2.8 × 10^-3 s^-1, highlighting its superior intrinsic activity. In addition, a symmetrical urea electrolyzer constructed using Fe₃O₄/NF produced the current density of 10 mA cm^-2 at a cell voltage of 1.54 V.

Phytate-coordinated nickel foam with enriched NiOOH intermediates for 5-hydroxymethylfurfural electrooxidation

Manipulating the surface reconstruction of Ni-based catalysts to form NiOOH intermediates is crucial for electrooxidation. Herein, we report a phytate coordination-induced enrichment of NiOOH on phytate-coordinated Ni foam, which exhibited high catalytic performance for 5-hydroxymethylfurfural electro-oxidation. The HMF oxidation rate of 0.76 mmol h^-1 outperformed the majority of Ni-based catalysts.

Hollow carbon spheres loaded with NiSe2 nanoplates as multifunctional SeS2 hosts for Li-SeS2 batteries

Selenium sulfide as a new alternative cathode material can effectively address the inferior electronic conductivity of sulfur, which is the main cause for poor electrochemical reactivity of conventional lithium-sulfur batteries (Li-S batteries). Therefore, in this work, hollow carbon spheres loaded with NiSe₂ nanoplates were prepared as SeS₂ hosts for Li-SeS₂ batteries. The unique micro-mesoporous hollow carbon spheres not only provide channels for the diffusion of SeS₂, but also afford spaces for alleviating the volume expansion of the active substance. Besides, the external polar NiSe₂ nanoplates increase active sites for capturing polysulfides or polyselenides during the charge/discharge process. Meanwhile, the excellent electronic conductivity of NiSe₂ can accelerate the catalytic reaction on the surface, thus reducing the loss of soluble intermediate products and finally suppressing the "shuttle effect". These extraordinary features of the as-proposed cathode offer many superiorities in electrochemical performances in terms of a high initial discharge capacity of 1139 mA h g^-1 at a current rate of 0.1C and an excellent cycling life of up to 1000 cycles at 1C.

In Situ Growth of S-Incorporated CoNiFe(oxy)hydroxides Nanoarrays as Efficient Multifunctional Electrocatalysts

Ni-, Co-based (oxy)hydroxides have received considerable attention as promising electrocatalysts for oxygen evolution reaction (OER), urea oxidation reaction (UOR), and even overall urea/water splitting. Constructing catalysts with special morphological and...

Cobalt, iron co-incorporated Ni(OH)2 multiphase for superior multifunctional electrocatalytic oxidation

The cobalt, iron co-incorporated Ni(OH)₂ multiphase displays superior catalytic activity and stability for multifunctional electrocatalytic oxidation, ascribed to the multiphase synergy, enhanced charge transfer and well-exposed active sites.

Noble-metal-free Cd0.3Zn0.7S-Ni(OH)2 for high efficiency visible light photocatalytic hydrogen production

Heterogeneously structured materials with supported precious metals, such as Pd, Pt, and Ru, as co-catalysts are important catalysts for efficient photocatalytic water splitting. However, the high costs and low reserves of precious metals have been an obstacle to their application in hydrogen production. In this work, the noble-metal-free Cd_0.3Zn_0.7S solid solution was designed and synthesized with an optimized molar ratio of Cd/Zn for the best visible light photocatalytic performance. In addition, a heterojunction hybrid material formed between the Cd_0.3Zn_0.7S and Ni(OH)₂ nanosheet was engineered to improve the utilization of light and to inhibit the recombination of holes and electrons. Ni(OH)₂ nanosheets assisted the transfer of the photoexcited electrons to participate in the reduction reactions which is critical for efficient and rapid catalytic hydrogen production. The photoelectrochemical property of the hybrid material was investigated with UV-vis absorption, photoluminance (PL) and electrochemical impedance spectroscopy measurements. The mechanism of the high-efficiency and low-cost photocatalytic hydrogen production was established by analyzing the hydrogen evolution kinetics. With the success of replacing precious metal with nickel-based surface heterostructure, this work is expected to provide a new type of photocatalyst for the application of photocatalytic hydrogen production.