Figure - available from: Nature Communications
This content is subject to copyright. Terms and conditions apply.
Photoelectrochemical performance aJ–V curves, b extracted Von, c chopped J–V curves, d local enlarged chopped J–V curves, e surface charge separation, f bulk charge separation, g ABPE, h IPCE, and i OCP-derived carrier lifetimes for Ta:Fe2O3, Ta:Fe2O3@Fe2O3, and NiFe(OH)x/Ta:Fe2O3@Fe2O3 photoanodes.
Source publication
Hematite has a great potential as a photoanode for photoelectrochemical (PEC) water splitting by converting solar energy into hydrogen fuels, but the solar-to-hydrogen conversion efficiency of state-of-the-art hematite photoelectrodes are still far below the values required for practical hydrogen production. Here, we report a core-shell formation o...
Citations
... This approach offers two significant advantages: firstly, it simplifies the preparation method as it utilizes the same material; secondly, gradient doping enables better lattice matching between junctions, thereby reducing charge recombination and loss. [97] For example, the gradient doping strategy can be used for the design of coreshell structures with lattice mismatches or with large band structure differences. [98] Zhang et al. [85] designed a CdS/CdSe x S 1-x core-shell quantum dots structure to modify TiO 2 photoanodes for application to PEC cells. ...
Photoelectrochemical (PEC) cells are regarded as a promising approach to convert sunlight to chemical fuels, whereas the serious photo‐induced charge recombination of the semiconductor photoelectrode hinders its solar conversion efficiency. Over the past few decades, designing and constructing heterojunction photoelectrodes via thermodynamically favorable charge transfer have been proven to be effective in boosting photo‐induced charge separation. However, the conventional heterojunction construction strategy generally introduces incompatible, nonconformal, or defective interfaces, leaving considerable room to improve the thermodynamically favorable charge transfer efficiency in the heterojunction photoelectrodes. To compensate for the unsatisfied charge transfer efficiency, some novel strategies, such as grain boundary engineering, band gap engineering, field‐effected engineering, etc., are adopted to provide additional charge transfer driving force, which significantly improves the charge transfer efficiency. In this review, these novel strategies are discussed beyond the conventional heterojunction construction, and the prospects for the development and applications of heterojunction photoanodes are also proposed.
... More importantly, compared to Fe 2 O 3 photoanode, Zn:Fe 2 O 3 shows lower trapping resistance (R trap ) at surface states and charge transfer resistance (R ct ) across the photoelectrode/electrolyte interface (Figure 4d,e). To further analyze the competing processes of charge transfer and surface recombination of surface states, which determine the rate of surface water oxidation in Fe 2 O 3 photoanode, we estimated the charge transfer efficiency using the Equation as follows: [36] Transfer efficiency (%) = k ct where k ct and k trap are the rate constants of charge transfer and trapping, respectively, assuming they are inversely proportional to their resistance. As shown in Figure 4f, the maximum charge transfer efficiencies obtained at ≈1.2 V RHE are 44.47 and 58.89% for Fe 2 O 3 and Zn:Fe 2 O 3 photoanodes, respectively. ...
Constructing an internal electric field (IEF) within the hematite (Fe2O3) photoanode for highly efficient water oxidation performance with facilitated charge transfer and separation remains still a significant challenge. Unlike the conventional approach of creating interfacial electric fields through heterojunction design by introducing another semiconductor, a novel strategy is proposed for engineering localized n‐p homojunctions on the surface of Fe2O3 photoanode using gradient Zn²⁺ doping strategy. By implementing this approach, the inherent n‐type characteristics of Fe2O3 can be transformed into p‐type, thereby facilitating the formation of an n‐p junction with robust IEF, which enables more efficient charge separation and transfer. Additionally, the gradient Zn²⁺ doping is accompanied by the generation of oxygen vacancies, which further improves the charge transfer efficiency and accelerates water oxidation kinetics. As expected, the photocurrent density of optimized Fe2O3 photoanode at 1.23 V versus reversible hydrogen electrode is ≈2.6‐fold that of Fe2O3. This work provides a novel perspective on the design of localized n‐p homojunction within photoanodes for achieving high solar energy conversion efficiency.
... These OCP transients were used to calculate OCP-derived charge carrier lifetimes ( n ) following previously published methods ( Figure S16b, Supporting Information). [8,50,51] ...
The increasing demand for clean hydrogen necessitates the rapid development of efficient photoanodes to catalyze the water oxidation half‐reaction effectively. Here a strategy is introduced to fabricate photoanodes that synergistically combine and leverage the properties of porous Ti‐doped hematite (Ti‐Fe2O3) and graphitic carbon nitride (g‐C3N4) nanosheets anchored with in situ grown Ni‐doped CoP co‐catalyst (Ni‐CoP). The resulting hybrid photoanodes exhibit >7 times higher photocurrent density at +1.23 VRHE compared with Ti‐Fe2O3 photoanodes. Comprehensive characterization techniques, including ambient photoemission spectroscopy, intensity‐modulated photocurrent spectroscopy, and transient absorption spectroscopy complementarily reveal the key impact of g‐C3N4 in these composites with enhanced solar oxygen evolution reaction: The incorporation of g‐C3N4 leads to enhanced charge separation through a type‐II heterojunction, thereby increasing the hole flux at the surface, and extending the charge carrier lifetime to the ms‐s range needed for water oxidation. Additionally, g‐C3N4 facilitates efficient transfer of photogenerated holes to the fine Ni‐CoP nanoparticles confined in the graphitic matrix for a boosted oxygen evolution reaction. These findings highlight the advantages of complex heterostructure photoanodes and demonstrate a new application of g‐C3N4 as a multifunctional support of co‐catalysts for future photoanodes with enhanced performance.
... The short carrier lifetime derived by the faster carrier relaxation after light-off implies that photogenerated carriers are efficiently transported to CPF-TTB under illumination. [50,51] The expedited decay kinetics of CPF-TTB/Ta 3 N 5 /TiN also corroborate the reduced charge recombination in the depletion region and the hole transport capability of CPF-TTB. ...
Discovering a competent charge transport layer promoting charge separation in photoelectrodes is a perpetual pursuit in photoelectrochemical (PEC) water splitting to achieve high solar‐to‐hydrogen (STH) conversion efficiency. Here, a conjugated polythiophene framework (CPF‐TTB) on Ta3N5 is elaborately electropolymerized, substantiating the hole transport behavior in their heterojunction. Tailored band structures of the CPF‐TTB/Ta3N5 reinforce the separation of photogenerated carriers, elevating a fill factor of the photoanode modified with a cocatalyst. The enhanced hole extraction enables the NiFeOx/CPF‐TTB/Ta3N5/TiN photoanode to generate a remarkable water oxidation photocurrent density of 9.12 mA cm⁻² at 1.23 V versus the reversible hydrogen electrode. A tandem device combining the photoanode with a perovskite/Si solar cell implements an unbiased solar water splitting with a STH conversion efficiency of 6.26% under parallel illumination mode. This study provides novel strategies in interface engineering for metal nitride‐based photoelectrodes, suggesting a promise of the organic–inorganic hybrid photoelectrode for high‐efficiency PEC water splitting.
... Although some chemical methods have been developed to produce various visible light responsive semiconductor photoactive films, including n-type BiVO 4 7,21,22 , Fe 2 O 3 8,9,23 , Ta 3 N 5 20 , and p-type Cu 2 O 10,24 , Sb 2 Se 3 25 , Cu 2 ZnSnS 4 26 semiconductors, post-treatments are generally indispensable to obtain the desired PEC performance, thus adding cost and complexity to these processes. Moreover, these post-treatments apparently increase the risk of photoelectrode heterogeneity, contributing to a marked decay of PEC activity when scaling up the working area, which has been frequently encountered in promising ...
The practical applications of solar-driven water splitting pivot on significant advances that enable scalable production of robust photoactive films. Here, we propose a proof-of-concept for fabricating robust photoactive films by a particle-implanting technique (PiP) which embeds semiconductor photoabsorbers in the liquid metal. The strong semiconductor/metal interaction enables resulting films efficient collection of photogenerated charges and superior photoactivity. A photoanode of liquid-metal embraced BiVO4 can stably operate over 120 h and retain ~ 70% of activity when scaled from 1 to 64 cm². Furthermore, a Z-scheme photocatalyst film of liquid-metal embraced BiVO4 and Rh-doped SrTiO3 particles can drive overall water splitting under visible light, delivering an activity 2.9 times higher than that of the control film with gold support and a 110 h stability. These results demonstrate the advantages of the PiP technique in constructing robust and efficient photoactive films for artificial photosynthesis.
... Therefore, Figure 6a suggests that the in situ implanted ZnO on g-C 3 N 4 sheets enhances the PEC-WS by improving the oxidizing power of photoinduced charges for promoting water oxidation compared to pristine ZnO and g-C 3 N 4 . 55 In addition, Figure 6b demonstrates that using TiO 2 photocatalyst as a current collector significantly increases the photovoltage of all photoanodes, underscoring the importance of TiO 2 in enhancing PEC-WS. Furthermore, the rapid decay of the potential observed for all TiO 2containing ZnO/g-C 3 N 4 composites upon turning off the light indicates rapid charge separation and migration on the ternary heterostructures containing Z-scheme ZnO/g-C 3 N 4 . ...
... Despite this rigorous structural requirement, that is, geometric dimensional matching at the unit-cell level, the textured growth of lattice-mismatched materials on TCOs is observed. For example, when deposited on tetragonal fluorine-doped tin oxide (FTO), hexagonal haematite (α-Fe 2 O 3 ), an extensively explored photoanode material in photoelectrochemical (PEC) water splitting [10][11][12] , usually shows a preferred [110] orientation, regardless of the synthesis procedures including spin coating, ultrasonic spray pyrolysis, hydrothermal techniques, pulsed laser deposition and so on [13][14][15][16][17] . Such phenomena imply that a unique coordination environment and interface structure develop between FTO and α-Fe 2 O 3 , which then fulfil the criteria for texture formation. ...
... Such phenomena imply that a unique coordination environment and interface structure develop between FTO and α-Fe 2 O 3 , which then fulfil the criteria for texture formation. Previous studies on the microstructure of α-Fe 2 O 3 photoanodes mainly focus on the crystallographic structure of grains 14,[17][18][19] . In-depth analyses of the practical interface structure (lattice arrangement and packing manner), local bond coordination characteristics between α-Fe 2 O 3 and FTO and understanding the growth mechanism of the [110]-oriented α-Fe 2 O 3 film on FTO (at the atomic scale) remain lacking. ...
Transparent conducting oxides are a critical component in modern (opto)electronic devices and solar energy conversion systems, and forming textured functional films on them is highly desirable for property manipulation and performance optimization. However, technologically important materials show varied crystal structures, making it difficult to establish coherent interfaces and consequently the oriented growth of these materials on transparent conducting oxides. Here, taking lattice-mismatched hexagonal α-Fe2O3 and tetragonal fluorine-doped tin oxide as the example, atomic-level investigations reveal that a coherent ordered structure forms at their interface, and via an oxygen-mediated dimensional and chemical-matching manner, that is, matched Voronoi cells of oxygen sublattices, [110]-oriented α-Fe2O3 films develop on fluorine-doped tin oxide. Further measurements of charge transport characteristics and photoelectronic effects highlight the importance and advantages of coherent interfaces and well-defined orientation in textured α-Fe2O3 films. Textured growth of lattice-mismatched oxides, including spinel Co3O4, fluorite CeO2, perovskite BiFeO3 and even halide perovskite Cs2AgBiBr6, on fluorine-doped tin oxide is also achieved, offering new opportunities to develop high-performance transparent-conducting-oxide-supported devices.
... Besides, the OCP transient decay measurement (Fig. S8 and SI) was used to evaluate the lifetime of photogenerated carriers. The strong band bending can create a large number of spatial charges in the depletion layer so that remarkable carrier recombination occurs immediately in the transient once illumination is turned off [53,54]. Thus, compared with TiO 2 (178 ms) and TB (128 ms), the fast decay kinetic constant of 72 ms further confirms effective charge separation due to the stronger band bending and built-in electric field in TBT3 [53,54]. ...
... The strong band bending can create a large number of spatial charges in the depletion layer so that remarkable carrier recombination occurs immediately in the transient once illumination is turned off [53,54]. Thus, compared with TiO 2 (178 ms) and TB (128 ms), the fast decay kinetic constant of 72 ms further confirms effective charge separation due to the stronger band bending and built-in electric field in TBT3 [53,54]. Besides, the significant decrease in the onset potential of TBT3 is also attributed to the larger DOCP provided by the stronger built-in electric field. ...
... Narrow band gap semiconductors, such as BiVO 4 , Ta 3 N 5 , etc., can extend the spectral absorption range to the visible region [65,66]; while wide band gap semiconductors, such as TiO 2 , ZnO, etc., can improve the light trapping ability [67,68]. Morphological control, metal/nonmetal doping and surface reconstruction, can accelerate the separation and transportation of photogenerated charges [69][70][71]. ...
Ammonia is a premium energy carrier with high content of hydrogen. However, energy storage and utilization via ammonia still confront multiple challenges. Here, we review recent progress and discuss challenges for the key steps of energy storage and utilization via ammonia (including hydrogen production, ammonia synthesis and ammonia utilization). In hydrogen production, we focus on important processes and catalytic designs for conversion of carbon feedstocks and water into hydrogen. To reveal crucial challenges of ammonia synthesis, catalytic designs and mechanisms are summarized and analyzed, in thermocatalytic synthesis, electrocatalytic synthesis and photocatalytic synthesis of ammonia. Further, in ammonia utilization, important processes and catalytic designs are outlined for ammonia decomposition, ammonia fuel cells and ammonia combustion. The goal of this review is to stimulate development of low-cost and eco-friendly ways for energy storage and utilization via ammonia.
... [23] It is worth noting that for bulk semiconductors, most of these introduced heteroatoms are situated in the body of the semiconductor rather than at the surface and have little chance to act as surface active sites, which limits the effect of doping strategy. [24,25] Whereas for ZnIn 2 S 4 , 2D layered structure endows it highly exposed surface atoms, thereby providing much more chance for the doped heteroatoms to expose at the surface of ZnIn 2 S 4 and directly in contact with electrolytes. Therefore, once these introduced doping sites can effectively trap photoholes and act as surface active sites to conduct photo-oxidation, the photocarrier separation efficiency and utilization efficiency can be evidently enhanced. ...
Fast recombination dynamics of photocarriers competing with sluggish surface photohole oxidation kinetics severely restricts the photoelectrochemical (PEC) conversion efficiency of photoanode. Here, a defect engineering strategy is developed to regulate photohole transfer and interfacial injection dynamics of 2D ZnIn2S4 (ZIS). Via selectively introducing substitutional Cd dopant at Zn sites of the ZIS basal plane, energy band structure and surface electrochemical activity are successfully modulated in the Cd‐doped ZIS (Cd‐ZIS) nanosheet array photoanode. Comprehensive characterizations manifest that a shallow acceptor level induced by Cd doping and superior electrochemical activity make surface Cd dopants simultaneously act as capture centers and active sites to mediate photohole dynamics at the reaction interface. In depth photocarrier dynamics analysis demonstrates that highly efficient photohole capture of Cd dopants brings about effective space separation of photocarriers and acceleration of surface reaction kinetics. Therefore, the optimum 2D Cd‐ZIS achieves excellent PEC solar energy conversion efficiency with a photocurrent density of 5.1 mA cm⁻² at 1.23 VRHE and a record of applied bias photon‐to‐current efficiency (ABPE) of 3.0%. This work sheds light on a microstructure design strategy to effectively regulate photohole dynamics for the next‐generation semiconducting PEC photoanodes.
