Quantum Dots‐Based Photoelectrochemical Hydrogen Evolution from Water Splitting

Abstract

opportunity since it is by far the most abundant, sustainable, carbon-neutral, and inexpensive energy source. The theoretical potential of solar power striking the earth's surface is ≈89 300 TW (the integral of the time-and-space-averaged solar flux 342.5 W m −2 over the earth's surface area 5.11 × 10 14 m 2 , estimating that ≈30% and ≈19% are scattered and absorbed by the atmosphere and clouds), [3] which is equivalent to ≈6000 times the power used worldwide every year (estimated at 13.5 TW in 2001, with projected growth up to 27.6 TW by 2050 by the Intergovernmental Panel on Climate Change). [4] In particular, storing solar energy in the form of H 2 presents advantages such as high energy content per mass (143 MJ kg −1), ease of transportation, and cost-effectiveness, [5] thereby addressing the storage challenge which is associated with the diffuse and intermittent character of solar irradiation. Solar energy and water could be converted into H 2 [5b] indirectly by using solar-converted electricity and an electrolyzer, [6] concentrated solar thermal and an electrolyzer, [7] biological and thermochemical processes [8] or directly by photo-/photoelectrocatalysis of water. [1b,f,g] The combination of the energy conversion step with electrolyzers is always limited by the performance of the electrolyzers, whose typical commercial efficiencies are around 73%. [9] Besides, indirect technologies suffer from excessive cost, area requirements, feasibility issues, or energy loss. [10] An alternative direct route is the photo-/photoelectrocatalysis of water, including powdered photocatalysts [11] and photoelectrochemical (PEC) cells. [12] The dispersion of powdered photocatalysts in water is suitable for large-scale processes, while the system requires stirring during the reaction and product separation after the reaction. In comparison, PEC systems (Figure 1a), which combine harvesting solar energy with water reduction into a single device, possesses several advantages. [13] i) PEC reactions address the issue of gas separation by generating products at different electrodes. ii) An external bias supply or self-bias voltage in the PEC system can provide additional energy input to compensate for the potential deficiency, [14] leading to the formation of a surface space charge layer and achieving efficient charge separation and an increased number of long-living photogenerated charges. [15] iii) Moreover, PEC systems can potentially be operated using only stable and abundant materials, such as Cu-based metal oxides, [16] Fe 2 O 3 , [14b,17] and TiO 2. [18] In a typical PEC system, at least one photoelectrode is used as a working electrode to harvest solar radiation, either acting Solar-driven photoelectrochemical (PEC) hydrogen evolution is a promising and sustainable approach to convert solar energy into a fuel that can be stored. Semiconductor quantum dots (QDs) are increasingly used in PEC devices due to their broad composition/size/shape tunable absorption spectrum (from ultraviolet to near-infrared, with significant over...

An efficient factor for fast screening of high-performance two-dimensional metal–organic frameworks towards catalyzing the oxygen evolution reaction

“…[1][2][3][4][5] Hydrogen, which is a kind of environmental-friendly energy carrier with high energy density, [6] has drawn increasing attention. [7,8] Water splitting has been widely considered to be a promising strategy to generate hydrogen [9][10] . However, electrocatalyzing oxygen evolution reaction (OER) is the efficiency-determining step of water splitting because OER is a multistep, four-electrons transfer process, which is a Gibbs free energy uphill process and then suffers from the slow kinetics and requires a high overpotential to drive the reaction.…”

Engineered Environment‐Friendly Colloidal Core/Shell Quantum Dots for High‐Efficiency Solar‐Driven Photoelectrochemical Hydrogen Evolution

“…[2] Owing to unique size/ shape/composition-tunable optoelectronic properties, semiconductor colloidal quantum dots (QDs) have attracted numerous attentions in optoelectronic applications in recent years, with specific developments in QDs-based PEC technologies, [3][4][5] which exhibit distinct advantages including cost-effectiveness, broad-band light absorbance, multiple exciton generation, and highefficiency charge transfer/separation. [6][7][8] Up to now, a large number of QDs, including PbS, CdSe, and CdS/CdSe, among others, have exhibited excellent performance when applied as light harvesters in the PEC devices. In particular, a PEC device fabricated from PbS/Mn-CdS QDs already established a record photocurrent density of around 22 mA cm À 2 .…”

Decoration of BiVO4 Photoanodes with Near-Infrared Quantum Dots for Boosted Photoelectrochemical Water Oxidation

“…However, it is worth noting that most of the highly active QDs used in PEC applications are still based on highly toxic Pb/Cd-based chalcogenides, and eco-friendly QD-based PEC systems have emerged recently, which are more promising for future commercial applications. 37 To the best of our knowledge, up to now, there are several cases reporting the construction of a heterojunction between BiVO 4 and QDs (e.g., CQDs/io-BiVO 4 , CQDs/BiVO 4 , ZnO-QDs/ BiVO 4 , CdTe-QDs/BiVO 4 , and graphene/ BiVO 4 ). 19,38−41 Although the abovementioned eco-friendly QDs (e.g., carbon/ZnO-QDs) have been selected to sensitize the BiVO 4 electrode, the utilization of solar absorption still needs to be enhanced, especially for the NIR region with a proportion of more than 50% energy in the solar spectrum.…”

“…, TiO 2 and ZnO) have demonstrated excellent PEC water oxidation performance after being incorporated with QDs. ,− Both heterojunction construction and band alignment matching are facile to implement between QDs and semiconductors. However, it is worth noting that most of the highly active QDs used in PEC applications are still based on highly toxic Pb/Cd-based chalcogenides, and eco-friendly QD-based PEC systems have emerged recently, which are more promising for future commercial applications …”