Monodispersed bimetallic nanoparticles anchored on TiO2-decorated titanium carbide MXene for efficient hydrogen production from hydrazine in aqueous solution
Graphical abstract
NiPt alloy NPs anchored on TiO2-decorated Ti3C2Tx MXene were synthesized and used as a highly efficient catalyst for hydrogen production from hydrazine.
Introduction
The continuous growth of global energy consumption has accelerated the development of energy production means [[1], [2], [3], [4]]. Compared with traditional hydrocarbon fuels such as gasoline (44 MJ/kg) and diesel (42 MJ/kg), hydrogen (H2) has a higher energy density (120 MJ/kg) and has broad application prospects in many fields, especially in the transportation industry [[5], [6], [7]]. However, the safe and efficient storage of hydrogen is the technical bottleneck in the large-scale application of hydrogen energy [[8], [9], [10], [11]]. Hydrous hydrazine (N2H4·H2O) has been considered as a liquid-phase chemical hydrogen storage material due to its high hydrogen storage density (8.0 wt%), convenient storage and transportation, easy recharging as a liquid, as well as the advantage of CO-free H2 production [[12], [13], [14], [15]]. Remarkably, when N2H4 completely decomposes to produce H2, the only by-product is N2 (eqn (1)). To effectively utilize hydrazine for hydrogen production, it is necessary to avoid the decomposition reaction in another way (eqn (2)) into the unwanted NH3 and N2 [16,17].N2H4 → N2 + 2H23N2H4 → N2 + 4NH3
To date, a lot of metallic catalysts have been developed toward the dehydrogenation of hydrazine [[18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29]]. For example, Xu and co-workers first reported that PtNi nanoparticles (NPs) stabilized by CTAB show 100% H2 selectivity for hydrazine decomposition [19]. Subsequently, it is found that these metallic NPs supported on carriers display exceptional performance in alkaline solution. Silica [20,21], zeolites [22,23], metal-organic frameworks [24,25], rare metal oxides [26,27], and reduced graphene oxides [28,29] have been widely applied as the support to immobilize the ultrafine metallic NPs. Previous works show that appropriate carrier could not only contribute to guarantee the excellent dispersion of the active metal NPs, but also have a positive impact on the catalytic performance through strong metal-support interaction. Thus, it is significant to find a matched carrier to support the metal NPs for improving the catalytic performance of the catalyst.
Recently, as a new type of ultrathin two-dimensional materials, MXene has been broadly studied because of its hydrophilicity, tunable interlayer spacing, and tailored surface chemistry [30]. The general formula of MXene is recorded as Mn+1XnTx (n = 1–3), where M stands for Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Mn, etc., X is the C or N element, and T stands for the surface chemical groups such as –OH, –O, and –F [31,32]. These characteristics provide many basic preconditions for regulating the conductivity and active sites of metal, and also provide a prospect for the application of MXene-based materials in advanced catalysis and energy fields [33,34]. Yoshimura’s group reported one-step hybridization to form Ag, Au, and Pd@MXene [35]. However, the unmodified MXene is difficult to effectively control the size of metal NPs so as to restricts its application. To fulfill the catalytic demand, the MXene-based materials that can stably disperse ultrafine metal NPs is highly desired.
Herein, we synthesized NiPt NPs supported on delamination of TiO2-decorated Ti3C2Tx (denoted as DT-Ti3C2Tx) nanosheets via a wet reduction method. The DT-Ti3C2Tx not only inherit the ultrathin properties of delaminated Ti3C2Tx (denoted as D-Ti3C2Tx) but also receive extra benefits such as high content of oxygen-containing functional groups and large surface area to prevent aggregation of metal NPs. In the reduction process, the interaction between oxygen-containing groups and precursors of metal NPs results in the formation of electron-rich NiPt NPs with outstanding dispersion and small size on DT-Ti3C2Tx. As a consequence, NiPt/DT-Ti3C2Tx shows excellent activity and stability in dehydrogenation of N2H4 and N2H4BH3 in aqueous solution.
Section snippets
Chemicals and materials
Rhodium(III) chloride trihydrate (RhCl3·3H2O, Rh: 38.5–42.5 wt%, Aladdin), ruthenium (III) chloride hydrate (RuCl3·xH2O, Ru basis: 36–40 wt%, Aladdin), sodium tetrachloropalladate (Na2PdCl4, 98%, Aladdin), irdium chloride hydrate (IrCl3·xH2O, Ir >52%, Aladdin), potassium tetrachloroplatinate (II) (K2PtCl4, 99.95%, J&K Chemical), silver nitrate (AgNO3, 99%, Aladdin), iron (IV) nitrate nonahydrate (Fe(NO3)3·9H2O), 98.5%, Aladdin), nickel (II) chloride hexahydrate (NiCl2·6H2O, 99.9%, Aladdin),
Synthesis and characterization of catalysts
NiPt NPs supported on DT-Ti3C2Tx nanosheets with a Ni/Pt molar ratio of 8/2 were selected as model catalyst for full characterization. Scheme 1 illustrates the synthesis of NiPt/DT-Ti3C2Tx nanocatalyst. Firstly, etched-Ti3C2Tx was prepared through HCl and LiF etching of the ternary transition metal carbides (MAX) phase (Ti3AlC2) to remove Al layers. D-Ti3C2Tx nanosheets were obtained by exfoliation of etched-Ti3C2Tx under ultrasonic. Then, metal salts were added to the flask under stirring
Conclusion
In summary, highly dispersed and electron-rich NiPt alloy NPs have been successfully immobilized on TiO2-decorated Ti3C2Tx MXene via a simple and general method. The NiPt alloy NPs with average size of 2.8 nm are uniformly dispersed on DT-Ti3C2Tx nanosheets. DT-Ti3C2Tx in the NiPt/DT-Ti3C2Tx act as electron donors to NiPt NPs for enhancing the electron density of NiPt NPs. Proper oxidation of Ti3C2Tx MXene could increase the number of oxygen-containing functional groups on Ti3C2Tx surface,
CRediT authorship contribution statement
Feng Guo: Conceptualization, Methodology, Investigation, Writing - original draft. Hongtao Zou: Validation, Writing - review & editing. Qilu Yao: Writing - review & editing. Bin Huang: Resources, Data curation. Zhang-Hui Lu: Supervision, Project administration, Funding acquisition, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This work was financially supported by the National Natural Science Foundation of China (Nos. 21763012 and 21802056), and the Natural Science Foundation of Jiangxi Province of China (Nos. 20181BAB213005 and 20192BAB203009).
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