- Award ID(s):
- 1752340
- NSF-PAR ID:
- 10082423
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 6
- Issue:
- 44
- ISSN:
- 2050-7488
- Page Range / eLocation ID:
- 22287 to 22300
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Two-dimensional (2D) molybdenum disulfide (MoS 2 ) has been recognized as a potential substitution of platinum (Pt) for electrochemical hydrogen evolution reaction (HER). However, the broad adoption of MoS 2 is hindered by its limited number of active sites and low inherent electrical conductivity. In this work, we employed a one-step solvothermal synthesis technique to construct a ternary hybrid structure consisting of dual-phase MoS 2, titanium carbide (Ti 3 C 2 ) MXene, and carbon nanotubes (CNTs), and demonstrated synergistic effects for active site exposure, surface area enlargement, and electrical conductivity improvement of the catalyst. The dual-phase MoS 2 (DP-MoS 2 ) is directly formed on the MXene with CNTs acting as crosslinks between 2D islands. The existence of edge-enriched metallic phase MoS 2 , the conductive backbone of MXene along with the crosslink function of CNTs clearly improves the overall HER performance of the ternary nanocomposite. Moreover, the integration of MoS 2 with MXene not only increases the interlayer distance of the 2D layers but also partially suppresses the MXene oxidation and the 2D layer restacking, leading to good catalytic stability. As a result, an overpotential of 169 mV and a low Tafel slope of 51 mV/dec was successfully achieved. This work paves a way for 2D-based electrocatalyst engineering and sheds light on the development of the next-generation noble metal-free HER electrocatalysts.more » « less
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Abstract Photoelectrodes without a p–n junction are often limited in efficiency by charge recombination at semiconductor surfaces and slow charge transfer to electrocatalysts. This study reports that tin oxide (SnO
x ) layers applied to n‐Si wafers after forming a thin chemically oxidized SiOx layer can passivate the Si surface while producing ≈620 mV photovoltage under 100 mW cm−2of simulated sunlight. The SnOx layer makes ohmic contacts to Ni, Ir, or Pt films that act as precatalysts for the oxygen‐evolution reaction (OER) in 1.0m KOH(aq) or 1.0m H2SO4(aq). Ideal regenerative solar‐to‐O2(g) efficiencies of 4.1% and 3.7%, respectively, are obtained in 1.0m KOH(aq) with Ni or in 1.0m H2SO4(aq) with Pt/IrOx layers as OER catalysts. Stable photocurrents for >100 h are obtained for electrodes with patterned catalyst layers in both 1.0m KOH(aq) and 1.0m H2SO4(aq). -
Abstract Nanoparticles supported on carbonaceous substrates are promising electrocatalysts. However, achieving good stability for the electrocatalysts during long‐term operations while maintaining high activity remains a grand challenge. Herein, a highly stable and active electrocatalyst featuring high‐entropy oxide (HEO) nanoparticles uniformly dispersed on commercial carbon black is reported, which is synthesized via rapid high‐temperature heating (≈1 s, 1400 K). Notably, the HEO nanoparticles with a record‐high entropy are composed of ten metal elements (i.e., Hf, Zr, La, V, Ce, Ti, Nd, Gd, Y, and Pd). The rapid high‐temperature synthesis can tailor structural stability and avoid nanoparticle detachment or agglomeration. Meanwhile, the high‐entropy design can enhance chemical stability to prevent elemental segregation. Using oxygen reduction reaction as a model, the 10‐element HEO exhibits good activity and greatly enhances stability (i.e., 92% and 86% retention after 12 and 100 h, respectively) compared to the commercial Pd/C electrocatalyst (i.e., 76% retention after 12 h). This superior performance is attributed to the high‐entropy compositional design and synthetic approach, which offers an entropy stabilization effect and strong interfacial bonding between the nanoparticles and carbon substrate. The approach promises a viable route toward synthesizing carbon‐supported high‐entropy electrocatalysts with good stability and high activity for various applications.
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It has been challenging to synthesize p-type SnOx(1≤x<2) and engineer the electrical properties such as carrier density and mobility due to the narrow processing window and the localized oxygen 2p orbitals near the valence band.
We recently reported on the processing of p-type SnOx and an oxide-based p-n heterostructures, demonstrating high on/off rectification ratio (>103), small turn-on voltage (<0.5 V), and low saturation current (~1×10-10A)1. In order to further understand the p-type oxide and engineer the properties for various electronic device applications, it is important to identify (or establish) the dominating doping and transport mechanisms. The low dopability in p-type SnOx, of which the causation is also closely related to the narrow processing window, needs to be mitigated so that the electrical properties of the material are to be adequately engineered2, 3.
Herein, we report on the multifunctional encapsulation of p-SnOxto limit the surface adsorption of oxygen and selectively permeate hydrogen into the p-SnOxchannel for thin film transistor (TFT) applications. Time-of-flight secondary ion mass spectrometry measurements identified that ultra-thin SiO2as a multifunctional encapsulation layer effectively suppressed the oxygen adsorption on the back channel surface of p-SnOxand augmented hydrogen density across the entire thickness of the channel. Encapsulated p-SnOx-based TFTs demonstrated much-enhanced channel conductance modulation in response to the gate bias applied, featuring higher on-state current and lower off-state current. The relevance between the TFT performance and the effects of oxygen suppression and hydrogen permeation is discussed in regard to the intrinsic and extrinsic doping mechanisms. These results are supported by density-functional-theory calculations.
Acknowledgement This work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 20011028) by KRISS. K.N. was supported by Basic Science Research Program (NRF-2021R11A1A01051246) through the NRF Korea funded by the Ministry of Education.
References Lee, D. H.; Park, H.; Clevenger, M.; Kim, H.; Kim, C. S.; Liu, M.; Kim, G.; Song, H. W.; No, K.; Kim, S. Y.; Ko, D.-K.; Lucietto, A.; Park, H.; Lee, S., High-Performance Oxide-Based p–n Heterojunctions Integrating p-SnOx and n-InGaZnO.
ACS Applied Materials & Interfaces 2021, 13 (46), 55676-55686.Hautier, G.; Miglio, A.; Ceder, G.; Rignanese, G.-M.; Gonze, X., Identification and design principles of low hole effective mass p-type transparent conducting oxides.
Nat Commun 2013, 4 .Yim, K.; Youn, Y.; Lee, M.; Yoo, D.; Lee, J.; Cho, S. H.; Han, S., Computational discovery of p-type transparent oxide semiconductors using hydrogen descriptor.
npj Computational Materials 2018, 4 (1), 17.Figure 1
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