Efficient electrocatalysts at decreasing cost for ethylene glycol (EG) oxidation reaction are highly demanded for generating electricity out of direct EG fuel cells and producing hydrogen from EG electroreforming cells. In this work, carbon-supported Pd-Ag bimetallic catalysts (Pd x Ag y /C) with varying atomic ratios (x: y = 2: 1, 1: 1, 1: 2, 1: 3 and 1: 4) are synthesized by adding a Pd(II) precursor solution in a preformed Ag colloid in the presence of ascorbic acid followed by mixing with carbon black, and then are screened for EG electrooxidation in alkaline media. ICP-AES, TEM, XRD and XPS are used to characterize the obtained Pd x Ag y /C catalysts. The resulting Pd x Ag y nanoparticles exhibit similarly mean sizes of ca. 9.5 nm and an essentially alloy structure with a Pd surface enrichment rather than a typical Ag core-Pd shell structure. Electrocatalytic evaluation reveals that the as-synthesized Pd x Ag y /C catalysts display a "volcano" profile in terms of the Pd mass activity with increasing y: x value, and the Pd 1 Ag 3 /C yields the most enhanced and durable activity among all the catalysts examined. Both electronic and bifunctional effects may account for this enhancement based on the existing guideline for bimetallic catalysts.
Solar hydrogen and electricity are promising high energy-density renewable sources. Although photochemistry or photovoltaics are attractive routes, special challenge arises in sunlight conversion efficiency. To improve efficiency, various semiconductor materials have been proposed with selective sunlight absorption. Here, we reported a hybrid system synergizing photo-thermochemical hydrogen and photovoltaics, harvesting full-spectrum sunlight in a cascade manner. A simple suspension of Au-TiO 2 in water/methanol serves as a spectrum selector, absorbing ultraviolet-visible and infrared energy for rapid photo-thermochemical hydrogen production. The transmitted visible and near-infrared energy fits the photovoltaic bandgap and retains the high efficiency of a commercial photovoltaic cell under different solar concentration values. The experimental design achieved an overall efficiency of 4.2% under 12 suns solar concentration. Furthermore, the results demonstrated a reduced energy loss in full-spectrum energy conversion into hydrogen and electricity. Such simple integration of photo-thermochemical hydrogen and photovoltaics would create a pathway toward cascading use of sunlight energy.
Currently, the production of solar fuels by the photoreduction of CO 2 with H 2 O is limited by the slow reaction rate and low efficiency of solar energy conversion. Combining concentrated solar power and plasmonic nanomaterials is a promising strategy to enhance photothermal transformation and promote solarto-fuel conversion. Herein, a nanocatalyst comprising gold anchored on TiO 2 was fabricated using a regular deposition-precipitation method. The nanocatalyst showed improved performance in CO 2 reduction with H 2 O under concentrated full-spectrum irradiation owing to the coupling of photo-and thermal energies. Macroscopic experiments demonstrated a clear correlation between the light intensity and the syngas yield, and a CO 2 conversion rate of 6.35% was achieved after 3 h under simulated sunlight illumination of 1644 mW/cm 2 . Photoelectrochemical measurements and finite element method simulations indicated that Au/TiO 2 achieved better separation and transport of the photoexcited carriers than TiO 2 owing to localized surface plasmon resonance that heats the nanocatalysts under concentrated full-spectrum irradiation. In situ diffuse reflectance infrared Fourier transform spectroscopy analysis also suggested that the photothermal effect accelerates the formation of intermediates such as formate and acetate and therefore enhances the overall photocatalytic rate. These results highlight the excellent potential of combining concentrated solar power and plasmonic nanostructures to realize the synergistic utilization of photon energy and thermal energy. Such a combination not only promotes the solar-to-fuel conversion efficiency but also paves the way for future applications in large-scale scenarios.
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