Photocathode Materials

Version	Summary	Created by	Modification	Content Size	Created at	Operation
1		Mohit Kumar	--	3315	2022-11-04 14:35:08	\|
2	format correct	Catherine Yang	+ 1 word(s)	3316	2022-11-07 04:16:50	\| \|
3	format correct	Catherine Yang	Meta information modification	3316	2022-11-07 04:17:21	\|

This entry is adapted from the peer-reviewed paper 10.3390/catal12101198

Photoelectrochemical water splitting is a promising approach to sustainable hydrogen production with no carbon emissions. Hydrogen being a future fuel to coming human generations is of utmost importance. The photocathodes in a photoelectrochemical (PEC) water-splitting cell are essential for the direct evolution of hydrogen. Among the known photocathodes, Cu-based p-type semiconducting materials are the most promising photo-absorber materials owing to their low-cost, low toxicity, natural abundance, suitable band-gaps, and favorable band edges for reduction.

photocathode H2 production PEC cocatalyst Hydrogen Nanomaterials

1. Introduction

The global energy demand is rising daily, while the supply comes from the same non-renewable energy sources ^[1]. Carbon emissions and environmental damage are liabilities of the energy derived from fossil fuels. However, the diminishing fossil fuel sources do not provide a steady fuel supply to meet the growing population and demand. Alternative energy sources should be considered to mitigate the impact of carbon emissions and meet the energy demand. H₂ is considered a fuel for future generations with a high energy density and a lower molecular weight. At the moment, the majority of H₂ is being produced using non-renewable sources of energy processes, such as steam methane reforming, coal gasification, and coal pyrolysis. In comparison, renewable sources of H₂ production include biomass gasification & pyrolysis, thermochemical, solar-driven plasmolysis, and photo-electrolysis ^[2]. Presently, renewable energy sources are being scrutinized for developing reliable energy sources with no carbon emissions and a sustainable environment ^[3]^[4]. Solar energy-based technologies are attracting a vast number of applications in the form of renewable sources of energy. Solar-driven water splitting, or photoelectrochemical (PEC) water splitting, is one of the most attractive techniques used to decompose water into hydrogen (H₂) and oxygen (O₂) ^[5]^[6]. The energy falling on the earth’s surface from solar radiation is a driving force for H₂ production. PEC cells use photoactive materials coated over a transparent conductive oxide surface, mainly known as a photoanode (where oxidation of water occurs on the surface resulting in the oxygen evolution reaction OER) and photocathode (where water reduction occurs on the surface, resulting in hydrogen evolution reaction (HER)) ^[7]^[8]. The photoactive material coated films over the photoanode are generally n-type semiconductor materials and p-type semiconductor materials on the photocathode.

PEC water splitting is also known as “artificial photosynthesis.” The concept of this phenomenon is nature-inspired plant leaves that convert solar light into carbohydrates. The sunlight absorbed by plant leaves is utilized by photosystem I (PS I) and photosystem II (PS II) to generate and transfer electrons through a series of transfer processes across several redox systems, to reduce CO₂ to hydrocarbons ^[9]. Similarly, semiconductors, absorbing the minimum threshold wavelength of light equivalent to their bandgaps, generate photoexcited electron/hole (e⁻/h⁺) pairs, and the photoexcited electrons are diffused to the conduction band. Holes remain in the valence band of semiconductors, and electrons travel to the surface of the photocathode. The HER and OER occur on the surface of the photoelectrodes, and the active surface sites govern the kinetics of the reaction. The active surface sites contribute toward the adsorption of H⁺ and OH− molecules on the surface of the photoelectrodes ^[10]^[11]^[12].

The seminal report on PEC water splitting, in 1972, used a thin layer of TiO₂ (E_g ~ 3.2 eV) as a photoanode for a PEC half-cell. Since then, photoanodes have been studied extensively with several material modifications and fabrication techniques. The OER takes place on the photoanode while the H₂ evolution occurs on the counter electrode ^[13]. The n-type semiconductors, such asTiO₂ (3.2–3.4 eV) ^[14], BiVO₄ (2.2–2.4 eV) ^[15], WO₃ (2.6–3 eV) ^[16], g-C₃N₄ (2.5–2.8 eV) ^[17], CdS (2.2–2.4 eV) ^[18], SrTiO₃ (3.2–3.4 eV), and Fe₂O₃ (2–2.2 eV) have been widely applied for the photoanode application in the PEC cell. Among all of these materials, TiO₂ comes out as the best material in terms of stability, while BiVO4 is the best material in abundance and light-absorbing capacity in the visible region ^[19].

Moreover, photocathodes have received very little attention when compared to photoanodes. Meanwhile, the direct evolution is more crucial than indirect evolution of H_2, which occurs in the photoanodic half-cells. Developing a p-type semiconductor material with a suitable bandgap, band alignment, and stability toward the oxidizing environment is paramount. Along with these physical and optical characteristics, the semiconductor must be tested for applications using non-precious and earth-abundant metals that are neither poisonous nor harmful with a sustainable approach^[20]^[21]^[22]^[23]^[24].

Copper-based oxide/chalcogenide semiconductor materials are promising materials owing to their tunable band gaps, band alignment with respect to water reduction potential (Figure 1), absorption coefficients, and various synthesis procedures. In this entry, the researchers have discussed recent advancements in the synthesis and fabrication of earth-abundant copper-based oxides/chalcogenides as a functional photocathode material for solar-driven water splitting, in light of their prospective use in PEC solar-to-hydrogen systems. In addition, several modifications that took place over a period and critically assess the ongoing debates in this area, have been discussed. Finally, this evaluation provides a chance to compare Cu-based semiconductor materials to give increasing emphasis to visible light-driven solar water electrolysis.

Figure 1. Energy band diagram of the various Cu-based binary, ternary, and quaternary metal oxides and sulfides.

2. Photocathode in a PEC Cell

Photocathodes are responsible for the reduction in a PEC cell serving the purpose of the direct evolution of hydrogen in a 2e⁻ transfer process over its surface. The minority charge carriers drive the reaction on the surface of the photoelectrode. To date, a number of materials have been investigated as efficient photocathodes for hydrogen generation such as p-Si (E_g = 1.1 eV) with a theoretical maximum photocurrent density −44 mA/cm² ^[25], InP (E_g = 1.3 eV) with a theoretical maximum photocurrent of −35 mA/cm² ^[26], p-GaP (E_g = 2.2 eV) ^[27] Sb₂Se₃ (E_g = 1.2 eV) ^[28], BiSbS₃, a p-type material with narrow bandgap (E_g = 2.2 eV)^[29]. Cu-based photocathode materials have a suitable conduction band maximum for the reduction of H⁺ ions and bandgap. The non-toxicity, earth abundance, low-cost, high absorption coefficient, and ease of synthesis make them a promising and sustainable component for photoabsorber materials. The sluggish reaction kinetics of the HER and the recombinations require the engineering of the interfaces with the different layers which give several advantages.

3. Photocathode Materials

3.1 Cu-Based Metal Oxides for the Photocathode

Copper-based metal oxides, such as Cu₂O and CuO are among the studied metal oxides, owing to their non-toxicity, availability, nature, and bandgaps. Due to their unique optoelectronic properties, they have been extensively used in energy conversion, storage, and sensing devices. However, the chemical instability of these materials restricts their PEC performance ^[30]. Cu₂O has a narrow bandgap (E_g = 2.0 eV) with a theoretical photocurrent density of −14 mA/cm² and a 18% photoconversion efficiency (PCE) owing to its light absorption in the AM 1.5 spectrum ^[31]. Cu₂O, as a photocatalyst, showed a stable H₂/O₂ evolution for 1900 h in visible light (λ > 460 nm) ^[32]. Although Cu₂O presents an immense opportunity for the hydrogen evolution, the photodegradation and recombination rate limits its photoactive material usage. Several strategies, including surface passivation, interfacial engineering, and cocatalyst decoration, have been investigated to overcome photodegradation and suppress the recombination to fabricate efficient photocathodes ^[33].

A Cu₂O/CuO heterojunction photocathode modified with a Cu₂S-Pt composite exhibited an enhanced hydrogen evolution. The optimum Cu₂S and Pt used as cocatalysts deposited using SILAR and sputtering sequentially, facilitated the charge transport and suppressed recombination. Cu₂O/CuO/Cu₂S-9/Pt delivered J = −5.7 mA/cm² at 0 V_RHE (2.5 times of Cu₂O/CuO), while a higher onset potential (E_op) for Cu₂O/CuO/Cu₂S−9/Pt was ~0.64 V_RHE observed, compared to Cu₂O/CuO (E_op = 0.54 V_RHE). The excessive Cu₂S deposition resulted in a parasitic light absorption and the creation of the recombination centers, resulting in J_ph fading ^[34].

The back contact material is essential in suppressing the recombination and charge transfer. Au is the best contact material for Cu₂O due to its large work function aligned with the valence band of Cu₂O. Recently, a CuO/NiO-based composite was investigated in place of Au using sputtering and aerial oxidation for the back contact with Cu₂O. A CuO/NiO thin film significantly improved and enhanced the transparency and hole collection (electron blocking) at the back contact of the Cu₂O photocathodes ^[35].

CuO is a p-type semiconductor with a narrow bandgap (E_g = 1.3–1.7 eV) suitable for light absorption and H₂ evolution. However, the photo corrosion of CuO in the presence of light is a significant drawback for the application. The majority of J_ph for the CuO photocathode is due to the photo corrosion of CuO to Cu with a low faradaic efficiency of the HER (0.01%) ^[36]. The deposition of CdS (buffer layer) and TiO₂ (as a protective layer), and Pt as a cocatalyst sequentially resulted in an enhanced PEC performance and faradaic efficiency (~100%) ^[36]. Various methods have been developed to synthesize CuO having different morphologies and bandgaps. The synthesis of CuO layers using sputtering and using variable power and thickness, exhibited a different photoactivity for hydrogen evolution. The variable power of sputtering (i.e., 30, 100, 200, and 300 W) in the synthesis resulted in a different morphology of the fabricated films, while the thickness of the layer of CuO played a role in light absorption. PXRD patterns showed the poor crystallinity of CuO due to low kinetic energy for diffusion and formation of Cu-O bond, while at higher the sputtering power, good crystalline films were obtained ^[37]. The deposition of a protective and stable metal oxide layer has proven to improve the faradaic efficiency of the H₂ evolution. The CuO/CuFe₂O₄ heterostructure was fabricated using the ion impregnation method. Although the faradaic efficiency increased from 45% for the bare CuO nanowires to 100% for CuO/CuFe₂O₄ with an improved stability, Jph decreased to one-third of the initial J_ph ^[38]. Generating Defects in the crystal structure (e.g., copper vacancies (V_Cu) in CuO) is an effective way to improve the charge separation and transfer. A study showed that V_Cu in CuO can be tuned by changing the O₂ partial pressure in the annealing process. The creation of vacancies in CuBi₂O₄ and CuFe₂O₄ resulted in an enhanced carrier concentration ^[39].

The incorporation of a foreign metal ion in the crystal structure can mitigate the issue of a photoinduced degradation. Several mixed metal oxides have been synthesized, such as CuBi₂O₄ ^[40], CuFe₂O₄ ^[41], CuAl₂O₄ ^[42], CuNbO₃ ^[43], and CuCrO₂ ^[44]_, and tested for the PEC photocathode application. CuBi₂O₄ has a bandgap of 1.5–1.8 eV and is a p-type mixed-metal oxide semiconductor that can be produced at low cost and with little environmental impact. By contributing their conduction band (CB) from the secondary metal rather than Cu 3d, ternary oxides have an advantage over the binary copper oxides in that they improve the photostability by preventing the conversion of Cu²⁺ to Cu⁰. CuBi₂O₄ is regarded as a good photocathode material because of its advantageous narrow bandgap, band positions, low cost, visible light absorption, non-toxicity, and high flat band potential (E_fb) values (>1 V vs. RHE), which are advantageous for unaided solar water splitting with a small bias given by the tandem photoanode. The theoretical photocurrent density reported for CuBi₂O₄ under AM 1.5 G (19.5–24.5 mA/cm²) is very far from achieved ^[45]. The practical photocurrent densities of the CuBi₂O₄ photocathodes are lower due to their poor charge transport, lower absorption coefficient, and higher charge recombination rates. Doping Ag⁺ in CuBi₂O₄ replacing Bi³⁺ increased the hole concentration, suppressing the anodic photo corrosion ^[46]. The sandwiched metal NPs between the heterojunction is a new approach for different configurations of the photocathode, which have shown potential in boosting the PEC performance. The PEC performance of the N,Cu-Codoped Carbon Nanosheets/Au/CuBi₂O₄ photocathode was examined. Au served as a plasmonic sensitizer and electron relay to transfer the charge from CuBi₂O₄ to the N,Cu-Codoped Carbon nanosheets ^[47].

Ferrites are considered one of the best candidates, owing to their merits, including earth abundance, non-toxicity, and stability in aqueous solutions. They have narrow band gaps and suitable band positions to drive the redox reaction over their surface ^[48]. Copper ferrite (CuFe₂O₄) is a mixed metal oxide and p-type semiconductor material for the PEC photocathode with a narrow bandgap (E_g = 1.5–1.9 eV). Theoretically, it can yield a high J_ph (~27 mA/cm²) and a STH efficiency (~ 33%). Although CuFe₂O₄ is an excellent p-type material, the crystallization temperature is high (~800–1000 °C), concerning the glass transition temperature of FTO (~564 °C). Fabrication of the heterojunction with CuFe₂O₄ has been extensively examined for the enhanced charge separation. CuFe₂O₄/Amorphous MnO₂ (AMO) was examined for the H₂ evolution in the neutral electrolyte, and 502.8 μmol H₂ was evolved in 90 min for a 1:4 ratio of CuFe₂O₄/AMO, which is higher than CuFe₂O₄/TiO₂ (130 μmol/h) and CuFe₂O₄/g-C₃N₄ (76 μmol/h) ^[49]. Photonic crystals (PC), consisting of CuFeO₂ decorated microspheres served as self-light harvesting architectures, allowing a high transmittance (~76%) and an amplified light absorption. The synthesis proceeded over the silica microspheres and the polymer-assisted synthesis. The novel design exhibited −0.2 mA/cm² at 0.6 V_RHE ^[50].

3.2 Cu-Based Sulfides for Photocathode

Copper-based sulfides are promising semiconducting materials for several applications, including photovoltaics, photo-electrocatalysis, energy storage, energy conversion, sensing, CO₂ reduction, and organic degradation. Cu₂S and CuS are the most sought out of the studied materials in the recent past. Recently, copper-based ternary sulfides such as CuInS₂, CuSbS₂, CuGaS₂, and CuFeS_2, and quaternary sulfides such as CuInGaS₂, Cu₂BaSnS4, and Cu₂ZnSnS₄ have gained much attention in solar cells and PEC water splitting. Their high absorption coefficient, tunable bandgaps, optical properties, suitable band positions for a redox reaction, and tunable crystal structure make them the most prominent candidates for their application in solar harvesting. These copper-based sulfides lack photostability and crystal defects which create recombination centers. The most prominent problem is the leaching of sulfides in harsh conditions, which is the major drawback in their application in photocathodes. The scarce availability and cost aspect of In and Ga in CuInGaS₂ is a major drawback for its large-scale production. Researchers have developed techniques, such as the heterojunction formation, doping, metal ion substitution, creating vacancies, decoration of plasmonic metal NPs, a passivation layer, and cocatalysts to enhance the PEC performance of photoelectrodes. Engineering the surface of the photoactive material with novel robust architectures and the deposition of interlayers, such as an electron transporting layer (ETL), hole transporting layer (HTL), cocatalysts, and passivation layers which inhibit the direct contact of electrolytes with the photoactive semiconductor, is required. The deposited layers must have a good optical transparency and little to no parasitic absorption of light.

Cu₂S is a p-type material with a narrow bandgap (E_g = 1.6–2 eV) with a remarkable absorption coefficient. Cu₂S can be synthesized through various processes such as annealing, hydrothermal, hot injection method, electrodeposition, sulfurization, etc. Cu₂S nanowires arrays (NWAs) synthesized via a self-growth mechanism over the Cu foil followed by the decoration of carbon quantum dots (CQDs) remarkably enhanced the PEC performance four times that of the pristine Cu₂S NWAs ^[51]. Cu_xS (0 < x ≤ 1) NPs with a copper deficiency show an inherent localized plasmonic resonance ^[52]. A novel solution processed ion exchange reaction to fabricate the Cu₂S films from the chemical bath deposited CdS films showed remarkable J_ph and PEC performances.

Ternary sulfides have an appropriate energy band structure, a wide photo-absorption range, and fast charge carrier dynamics due to the less positive valence occupied by the S 3p orbital (when compared to O 2p) and small effective mass carriers, making them promising alternatives in photovoltaic, photocatalytic, and PEC devices. For instance, altering the rate of cation exchange or the proportion of the sulfur precursor during the synthesis process, may be used to create ternary Cu-In-S materials with various crystal morphologies, compositions, and switchable n-type and p-type semiconducting characteristics ^[53]. CuInS₂ (E_g ~ 1.5–1.8 eV) is a photoactive material in solar cells and PEC photocathodes. Along with the merits, CuInS₂ suffers from a high rate of recombination. Therefore, the CuInS₂-based photocathodes have been modified with other materials to improve PCE. Fabrication of the heterojunction generates an inbuilt electric field that helps in the charge separation and the enhanced light absorption.

Recently, CuSbS₂ has gained attention in the PEC photocathodic approach. It has also been used as HTL in solar cells for the hole extraction ^[54]^[55]. Synthetic procedures include thermal evaporation ^[56]^[57], electrodeposition ^[58], sputtering ^[59], CBD ^[56], pyrolysis ^[60], etc. In a recent study, CuSbS₂ exhibited a temperature-dependent bandgap (E_g = 1.57–1.58 eV). A CuSbS₂/Sb₂Se₃/TiO_x/Pt photocathode was fabricated which exhibited a remarkable J_ph = −18 mA/cm² at 0 V_RHE in 1 M H₂SO₄. The CuSbS₂ film acted as a hole transporting layer and a photoactive material, suppressing the recombination rate. In another study, the facile heterojunction of CuSbS₂ with CdS was synthesized and examined for the PEC photocathode. CuSbS₂/CdS/Pt delivered J_ph = −4.1 mA/cm² at 0 V_RHE and E_op = 0.45 V_RHE ^[61].

Quaternary copper-based sulfides are the newly emerging most interesting p-type materials (e.g., Cu₂ZnSnS₄) with the promising potential for solar harvesting applications. Synthesis procedures involved in the fabrication of films are hydrothermal, molecular ink, electrodeposition, and vacuum-based synthesis. The rapid progress in materials to achieve the target efficiency of these sulfides are hindered by the narrow phase stability of the quaternary phase and the existence of secondary phases, such as ZnS, Cu₂S, SnS, SnS₂, and Cu₂SnS_3, and to defects leading to poor performance and repeatability ^[62]. In early reports, Mo/Cu₂ZnSnS₄/CdS/AZO/TiO₂/Pt was fabricated via electrodeposition (sequential and simultaneous). Moreover, the examined photocathode showed over −1 mA/cm² at 0 V_RHE in the simultaneous electrodeposition ^[63]. The buffer layer formed over Cu₂ZnSnS₄ was scrutinized with CdS and In₂S_3, and the Cu₂ZnSnS₄/CdS/In₂S₃/Pt fabricated showed a higher J_ph and PCE, as compared to Cu₂ZnSnS₄/CdS/Pt. The modification with an In₂S₃/CdS double layer followed by the deposition of Pt exhibited STH (%) ~ 1.63% ^[64]. A HfO₂ layer was particularly effective at surface passivating the CdS/Cu₂ZnSnS₄ photocathode, which increased the photoelectrochemical stability. With a 6 nm thick HfO₂ layer added, the CdS/Cu₂ZnSnS₄ photocathode demonstrated a long-term photocurrent stability of over 10 h while maintaining a high half-cell solar-to-hydrogen efficiency (HC-STH) of 2.7% at 0.36 V_RHE. A full PEC cell was fabricated using a BiVO₄-based photoanode ^[65]. The molecular ink-derived Cu₂ZnSnS₄ (CZTS) films were synthesized via spin coating. The study showed the sequence of the precursor addition in the 2-methoxyethanol (2-ME) and the films synthesized with the configuration CZTS/CdS/ALD-TiO₂/Pt. CdS served as a buffer layer, TiO₂ as a passivation layer, and Pt coated as a cocatalyst for the HER. CZTS/CdS/ALD-TiO₂/Pt delivered −21.5 mA/cm² at −0.2 V_RHE with a 40–45% faradaic efficiency, showing side reactions as the surface of CZTS is not fully covered ^[66].

The metal ion substitution has been studied and proved to improve the optical properties of Cu₂ZnSnS₄. The substitution of Cu with Ag and Zn with X (X = In⁺³, Cd⁺², Sb⁺³, Bi⁺³) have been studied extensively with the application in the PEC cells and solar cells. The photocurrent produced by a Cu₂Cd_0.4Zn_0.6SnS₄ (CCZTS) photoabsorber coated with CdS/TiMo/Pt is claimed to be −17 mA/cm² at 0 V_RHE, which is at least three times larger than the photocurrent produced by a pure Cu₂ZnSnS₄. The XPS studies revealed a 0.13 eV spike-like offset when integrated with CdS, which enhanced the charge separation and transfer ^[67]. A low Ag substitution in Cu₂ZnSnS₄ revealed an enhanced J_ph and E_op. Cu⁺ was partially substituted with Ag⁺ ion in the (Ag_xCu_1-x)₂ZnSnS₄ (x-ACZTS) (x = 0.04, 0.08, 0.10) crystal structure synthesized via a molecular ink precursor spin-coated over the transparent conductive oxide. In comparison to the CZTS/CdS/Pt photocathode, which has a photocurrent of −13 mA/cm² and an onset potential of 0.65 V_RHE, the ACZTS/CdS/Pt photocathode produces a maximum photocurrent of −17.7 mA/cm² at 0 V_RHE with 4% Ag (x = 0.04) and a maximum onset potential of 0.85 V_RHE with 8% Ag (x = 0.08) ^[68].

Another new class of materials when Zn is replaced with Ba in CZTS is an earth-abundant emerging material for PV applications ^[69]. Cu₂BaSnS₄ is a p-type material (E_g ~ 1.5–2.0 eV) with a readily available and cost-effective material that can be synthesized on a large scale. The maximum theoretical maximum J_ph obtained is −14 mA/cm², according to the Schokley–Queisser limit (Q–S limit) ^[70].

References

Waheed, R.; Sarwar, S.; Wei, C. The Survey of Economic Growth, Energy Consumption and Carbon Emission. Energy Rep. 2019, 5, 1103–1115.
Younas, M.; Shafique, S.; Hafeez, A.; Javed, F.; Rehman, F. An Overview of Hydrogen Production: Current Status, Potential, and Challenges. Fuel 2022, 316, 123317.
Staffell, I.; Scamman, D.; Abad, A.V.; Balcombe, P.; Dodds, P.E.; Ekins, P.; Shah, N.; Ward, K.R. The Role of Hydrogen and Fuel Cells in the Global Energy System. Energy Environ. Sci. 2019, 12, 463–491.
Sharif, A.; Raza, S.A.; Ozturk, I.; Afshan, S. The Dynamic Relationship of Renewable and Nonrenewable Energy Consumption with Carbon Emission: A Global Study with the Application of Heterogeneous Panel Estimations. Renew. Energy 2019, 133, 685–691.
Jacobsson, T.J. Photoelectrochemical Water Splitting: An Idea Heading towards Obsolescence? Energy Environ. Sci. 2018, 11, 1977–1979.
Walter, M.G.; Warren, E.L.; McKone, J.R.; Boettcher, S.W.; Mi, Q.; Santori, E.A.; Lewis, N.S. Solar Water Splitting Cells. Chem. Rev. 2010, 110, 6446–6473.
Sivula, K.; van de Krol, R. Semiconducting Materials for Photoelectrochemical Energy Conversion. Nat. Rev. Mater. 2016, 1, 15010.
Hisatomi, T.; Kubota, J.; Domen, K. Recent Advances in Semiconductors for Photocatalytic and Photoelectrochemical Water Splitting. Chem. Soc. Rev. 2014, 43, 7520–7535.
Whang, D.R.; Apaydin, D.H. Artificial Photosynthesis: Learning from Nature. ChemPhotoChem 2018, 2, 148–160.
Yang, Y.; Niu, S.; Han, D.; Liu, T.; Wang, G.; Li, Y. Progress in Developing Metal Oxide Nanomaterials for Photoelectrochemical Water Splitting. Adv. Energy Mater. 2017, 7, 1–26.
Chaves, A.; Azadani, J.G.; Alsalman, H.; da Costa, D.R.; Frisenda, R.; Chaves, A.J.; Song, S.H.; Kim, Y.D.; He, D.; Zhou, J.; et al. Bandgap Engineering of Two-Dimensional Semiconductor Materials. NPJ 2D Mater. Appl. 2020, 4, 29.
Su, J.; Vayssieres, L. A Place in the Sun for Artificial Photosynthesis? ACS Energy Lett. 2016, 1, 121–135.
Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37–38.
Subramanyam, P.; Kumar, P.N.; Deepa, M.; Subrahmanyam, C.; Ghosal, P. Bismuth Sulfide Nanocrystals and Gold Nanorods Increase the Photovoltaic Response of a TiO2/CdS Based Cell. Sol. Energy Mater. Sol. Cells 2017, 159, 296–306.
Subramanyam, P.; Vinodkumar, T.; Nepak, D.; Deepa, M.; Subrahmanyam, C. Mo-Doped BiVO4@reduced Graphene Oxide Composite as an Efficient Photoanode for Photoelectrochemical Water Splitting. Catal. Today 2019, 325, 73–80.
Subramanyam, P.; Meena, B.; Sinha, G.N.; Deepa, M.; Subrahmanyam, C. Decoration of Plasmonic Cu Nanoparticles on WO3/Bi2S3 QDs Heterojunction for Enhanced Photoelectrochemical Water Splitting. Int. J. Hydrogen Energy 2020, 45, 7706–7715.
Subramanyam, P.; Meena, B.; Suryakala, D.; Deepa, M.; Subrahmanyam, C. Plasmonic Nanometal Decorated Photoanodes for Efficient Photoelectrochemical Water Splitting. Catal. Today 2020, 379, 1–6.
Li, J.; Cushing, S.K.; Zheng, P.; Senty, T.; Meng, F.; Bristow, A.D.; Manivannan, A.; Wu, N. Solar Hydrogen Generation by a CdS-Au-TiO2 Sandwich Nanorod Array Enhanced with Au Nanoparticle as Electron Relay and Plasmonic Photosensitizer. J. Am. Chem. Soc. 2014, 136, 8438–8449.
Shi, H.; Guo, H.; Wang, S.; Zhang, G.; Hu, Y.; Jiang, W.; Liu, G. Visible Light Photoanode Material for Photoelectrochemical Water Splitting: A Review of Bismuth Vanadate. Energy Fuels 2022, 36, 11404–11427.
Yang, W.; Moon, J. Recent Advances in Earth-Abundant Photocathodes for Photoelectrochemical Water Splitting. ChemSusChem 2019, 12, 1889–1899.
Toe, C.Y.; Zhou, S.; Gunawan, M.; Lu, X.; Ng, Y.H.; Amal, R. Recent Advances and the Design Criteria of Metal Sulfide Photocathodes and Photoanodes for Photoelectrocatalysis. J. Mater. Chem. A 2021, 9, 20277–20319.
Li, X.; Yu, J.; Low, J.; Fang, Y.; Xiao, J.; Chen, X. Engineering Heterogeneous Semiconductors for Solar Water Splitting. J. Mater. Chem. A 2015, 3, 2485–2534.
Chen, Q.; Fan, G.; Fu, H.; Li, Z.; Zou, Z. Tandem Photoelectrochemical Cells for Solar Water Splitting. Adv. Phys. X 2018, 3, 1487267.
Prévot, M.S.; Sivula, K. Photoelectrochemical Tandem Cells for Solar Water Splitting. J. Phys. Chem. C 2013, 117, 17879–17893.
Lin, Y.; Battaglia, C.; Boccard, M.; Hettick, M.; Yu, Z.; Ballif, C.; Ager, J.W.; Javey, A. Amorphous Si Thin Film Based Photocathodes with High Photovoltage for Efficient Hydrogen Production. Nano Lett. 2013, 13, 5615–5618.
Lee, M.H.; Takei, K.; Zhang, J.; Kapadia, R.; Zheng, M.; Chen, Y.-Z.; Nah, J.; Matthews, T.S.; Chueh, Y.-L.; Ager, J.W.; et al. P-Type InP Nanopillar Photocathodes for Efficient Solar-Driven Hydrogen Production. Angew. Chem. Int. Ed. 2012, 51, 10760–10764.
Liu, C.; Sun, J.; Tang, J.; Yang, P. Zn-Doped p-Type Gallium Phosphide Nanowire Photocathodes from a Surfactant-Free Solution Synthesis. Nano Lett. 2012, 12, 5407–5411.
Yang, W.; Kim, J.H.; Hutter, O.S.; Phillips, L.J.; Tan, J.; Park, J.; Lee, H.; Major, J.D.; Lee, J.S.; Moon, J. Benchmark Performance of Low-Cost Sb2Se3 Photocathodes for Unassisted Solar Overall Water Splitting. Nat. Commun. 2020, 11, 861.
Meena, B.; Kumar, M.; Gupta, S.; Sinha, L.; Subramanyam, P.; Subrahmanyam, C. Rational Design of TiO2/BiSbS3 Heterojunction for Efficient Solar Water Splitting. Sustain. Energy Technol. Assessments 2022, 49, 101775.
Li, C.; He, J.; Xiao, Y.; Li, Y.; Delaunay, J.-J. Earth-Abundant Cu-Based Metal Oxide Photocathodes for Photoelectrochemical Water Splitting. Energy Environ. Sci. 2020, 13, 3269–3306.
Paracchino, A.; Laporte, V.; Sivula, K.; Grätzel, M.; Thimsen, E. Highly Active Oxide Photocathode for Photoelectrochemical Water Reduction. Nat. Mater. 2011, 10, 456–461.
Hara, M. Cu2O as a Photocatalyst for Overall Water Splitting under Visible Light Irradiation. Chem. Commun. 1998, 2, 357–358.
Ding, C.; Shi, J.; Wang, Z.; Li, C. Photoelectrocatalytic Water Splitting: Significance of Cocatalysts, Electrolyte, and Interfaces. ACS Catal. 2017, 7, 675–688.
Dubale, A.A.; Tamirat, A.G.; Chen, H.-M.; Berhe, T.A.; Pan, C.-J.; Su, W.-N.; Hwang, B.-J. A Highly Stable CuS and CuS–Pt Modified Cu2O/CuO Heterostructure as an Efficient Photocathode for the Hydrogen Evolution Reaction. J. Mater. Chem. A 2016, 4, 2205–2216.
Son, M.K.; Steier, L.; Schreier, M.; Mayer, M.T.; Luo, J.; Grätzel, M. A Copper Nickel Mixed Oxide Hole Selective Layer for Au-Free Transparent Cuprous Oxide Photocathodes. Energy Environ. Sci. 2017, 10, 912–918.
Septina, W.; Prabhakar, R.R.; Wick, R.; Moehl, T.; Tilley, S.D. Stabilized Solar Hydrogen Production with CuO/CdS Heterojunction Thin Film Photocathodes. Chem. Mater. 2017, 29, 1735–1743.
Masudy-Panah, S.; Moakhar, R.S.; Chua, C.S.; Tan, H.R.; Wong, T.I.; Chi, D.; Dalapati, G.K. Nanocrystal Engineering of Sputter-Grown CuO Photocathode for Visible-Light-Driven Electrochemical Water Splitting. ACS Appl. Mater. Interfaces 2016, 8, 1206–1213.
Cots, A.; Bonete, P.; Gómez, R. Improving the Stability and Efficiency of CuO Photocathodes for Solar Hydrogen Production through Modification with Iron. ACS Appl. Mater. Interfaces 2018, 10, 26348–26356.
Wang, Z.; Zhang, L.; Schülli, T.U.; Bai, Y.; Monny, S.A.; Du, A.; Wang, L. Identifying Copper Vacancies and Their Role in the CuO Based Photocathode for Water Splitting. Angew. Chem. 2019, 131, 17768–17773.
Nakabayashi, Y.; Nishikawa, M.; Nosaka, Y. Fabrication of CuBi2O4 Photocathode through Novel Anodic Electrodeposition for Solar Hydrogen Production. Electrochim. Acta 2014, 125, 191–198.
Park, S.; Baek, J.H.; Zhang, L.; Lee, J.M.; Stone, K.H.; Cho, I.S.; Guo, J.; Jung, H.S.; Zheng, X. Rapid Flame-Annealed CuFe2O4 as Efficient Photocathode for Photoelectrochemical Hydrogen Production. ACS Sustain. Chem. Eng. 2019, 7, 5867–5874.
Tan, R.; Hwang, S.W.; Sivanantham, A.; Cho, I.S. Solution Synthesis and Activation of Spinel CuAl2O4 Film for Solar Water-Splitting. J. Catal. 2021, 400, 218–227.
Crespo, C.T. CuNbO3 as a Solar Energy Converter to Fuel and Electricity. Sol. Energy Mater. Sol. Cells 2018, 179, 305–311.
Creissen, C.E.; Warnan, J.; Reisner, E. Solar H2 Generation in Water with a CuCrO2 Photocathode Modified with an Organic Dye and Molecular Ni Catalyst. Chem. Sci. 2018, 9, 1439–1447.
Monny, S.A.; Zhang, L.; Wang, Z.; Luo, B.; Konarova, M.; Du, A.; Wang, L. Fabricating Highly Efficient Heterostructured CuBi2O4 Photocathodes for Unbiased Water Splitting. J. Mater. Chem. A 2020, 8, 2498–2504.
Kang, D.; Hill, J.C.; Park, Y.; Choi, K.-S. Photoelectrochemical Properties and Photostabilities of High Surface Area CuBi2O4 and Ag-Doped CuBi2O4 Photocathodes. Chem. Mater. 2016, 28, 4331–4340.
Xu, N.; Li, F.; Gao, L.; Hu, H.; Hu, Y.; Long, X.; Ma, J.; Jin, J. N,Cu-Codoped Carbon Nanosheet/Au/CuBi2O4 Photocathodes for Efficient Photoelectrochemical Water Splitting. ACS Sustain. Chem. Eng. 2018, 6, 7257–7264.
Kim, J.H.; Kim, H.E.; Kim, J.H.; Lee, J.S. Ferrites: Emerging Light Absorbers for Solar Water Splitting. J. Mater. Chem. A 2020, 8, 9447–9482.
Atacan, K.; Topaloğlu, B.; Özacar, M. New CuFe2O4/Amorphous Manganese Oxide Nanocomposites Used as Photocatalysts in Photoelectrochemical Water Splitting. Appl. Catal. A Gen. 2018, 564, 33–42.
Oh, Y.; Yang, W.; Kim, J.; Jeong, S.; Moon, J. Enhanced Photocurrent of Transparent CuFeO2 Photocathodes by Self-Light-Harvesting Architecture. ACS Appl. Mater. Interfaces 2017, 9, 14078–14087.
Li, M.; Zhao, R.; Su, Y.; Yang, Z.; Zhang, Y. Carbon Quantum Dots Decorated Cu2S Nanowire Arrays for Enhanced Photoelectrochemical Performance. Nanoscale 2016, 8, 8559–8567.
Chen, L.; Hu, H.; Chen, Y.; Gao, J.; Li, G. Plasmonic Cu2-XS Nanoparticles: A Brief Introduction of Optical Properties and Applications. Mater. Adv. 2021, 2, 907–926.
Feng, X.; Li, R.; Wang, M.; Chen, Y. Switchable Synthesis of P- and n-Type Cu–In–S Grooved Pyramid-like Microcrystals for Unassisted Photoelectrochemical Water Splitting. J. Mater. Chem. A 2018, 6, 11180–11188.
Teimouri, R.; Mohammadpour, R. Potential Application of CuSbS2 as the Hole Transport Material in Perovskite Solar Cell: A Simulation Study. Superlattices Microstruct. 2018, 118, 116–122.
Ramasamy, K.; Tien, B.; Archana, P.S.; Gupta, A. Copper Antimony Sulfide (CuSbS2) Mesocrystals: A Potential Counter Electrode Material for Dye-Sensitized Solar Cells. Mater. Lett. 2014, 124, 227–230.
Macías, C.; Lugo, S.; Benítez, Á.; López, I.; Kharissov, B.; Vázquez, A.; Peña, Y. Thin Film Solar Cell Based on CuSbS2 Absorber Prepared by Chemical Bath Deposition (CBD). Mater. Res. Bull. 2017, 87, 161–166.
Medina-Montes, M.I.; Campos-González, E.; Morales-Luna, M.; Sánchez, T.G.; Becerril-Silva, M.; Mayén-Hernández, S.A.; de Moure-Flores, F.; Santos-Cruz, J. Development of Phase-Pure CuSbS2 Thin Films by Annealing Thermally Evaporated CuS/Sb2S3 Stacking Layer for Solar Cell Applications. Mater. Sci. Semicond. Process. 2018, 80, 74–84.
Rastogi, A.C.; Janardhana, N.R. Properties of CuSbS2 Thin Films Electrodeposited from Ionic Liquids as P-Type Absorber for Photovoltaic Solar Cells. Thin Solid Films 2014, 565, 285–292.
Wang, L.; Zhao, X.; Yang, Z.; Ng, B.K.; Jiang, L.; Lai, Y.; Jia, M. CuSbS2 Solar Cells Using CdS, In2S3 and the In/Cd-Based Hybrid Buffers. J. Electron. Mater. 2021, 50, 3283–3287.
Aquino, J.A.R.; Vela, D.L.R.; Shaji, S.; Avellaneda, D.A.; Krishnan, B. Spray Pyrolysed Thin Films of Copper Antimony Sulfide as Photovoltaic Absorber. Phys. Status Solidi C 2016, 13, 24–29.
Zhang, L.; Li, Y.; Li, X.; Li, C.; Zhang, R.; Delaunay, J.-J.; Zhu, H. Solution-Processed CuSbS2 Thin Film: A Promising Earth-Abundant Photocathode for Efficient Visible-Light-Driven Hydrogen Evolution. Nano Energy 2016, 28, 135–142.
Kumar, M.; Dubey, A.; Adhikari, N.; Venkatesan, S.; Qiao, Q. Strategic Review of Secondary Phases, Defects and Defect-Complexes in Kesterite CZTS-Se Solar Cells. Energy Environ. Sci. 2015, 8, 3134–3159.
Rovelli, L.; Tilley, S.D.; Sivula, K. Optimization and Stabilization of Electrodeposited Cu2ZnSnS4 Photocathodes for Solar Water Reduction. ACS Appl. Mater. Interfaces 2013, 5, 8018–8024.
Jiang, F.; Gunawan; Harada, T.; Kuang, Y.; Minegishi, T.; Domen, K.; Ikeda, S. Pt/In2S3/CdS/Cu2ZnSnS4 Thin Film as an Efficient and Stable Photocathode for Water Reduction under Sunlight Radiation. J. Am. Chem. Soc. 2015, 137, 13691–13697.
Huang, D.; Wang, K.; Yu, L.; Nguyen, T.H.; Ikeda, S.; Jiang, F. Over 1% Efficient Unbiased Stable Solar Water Splitting Based on a Sprayed Cu2ZnSnS4 Photocathode Protected by a HfO2 Photocorrosion-Resistant Film. ACS Energy Lett. 2018, 3, 1875–1881.
Yang, W.; Oh, Y.; Kim, J.; Jeong, M.J.; Park, J.H.; Moon, J. Molecular Chemistry-Controlled Hybrid Ink-Derived Efficient Cu2ZnSnS4 Photocathodes for Photoelectrochemical Water Splitting. ACS Energy Lett. 2016, 1, 1127–1136.
Tay, Y.F.; Kaneko, H.; Chiam, S.Y.; Lie, S.; Zheng, Q.; Wu, B.; Hadke, S.S.; Su, Z.; Bassi, P.S.; Bishop, D.; et al. Solution-Processed Cd-Substituted CZTS Photocathode for Efficient Solar Hydrogen Evolution from Neutral Water. Joule 2018, 2, 537–548.
Tay, Y.F.; Hadke, S.S.; Zhang, M.; Lim, N.; Chiam, S.Y.; Wong, L.H. Improving the Interfacial Properties of CZTS Photocathodes by Ag Substitution. J. Mater. Chem. A 2020, 8, 8862–8867.
Kumar, S.M.; Madhusudanan, S.P.; Rajamani, A.R.; Siaj, M.; Batabyal, S.K. Barium Substitution in Kesterite Cu2ZnSnS4: Cu2Zn1−xBaxSnS4 Quinary Alloy Thin Films for Efficient Solar Energy Harvesting. Cryst. Growth Des. 2020, 20, 4387–4394.
Todorov, T.; Gunawan, O.; Guha, S. A Road towards 25% Efficiency and beyond: Perovskite Tandem Solar Cells. Mol. Syst. Des. Eng. 2016, 1, 370–376.

© Text is available under the terms and conditions of the Creative Commons Attribution (CC BY) license; additional terms may apply. By using this site, you agree to the Terms and Conditions and Privacy Policy.

Upload a video for this entry

Information

Subjects: Materials Science, Composites; Chemistry, Physical; Green & Sustainable Science & Technology

Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :

Mohit Kumar

Bhagatram Meena

Palyam Subramanyam

Duvvuri Suryakala

Challapalli Subrahmanyam

View Times: 1.2K

Update Date: 08 Nov 2022

Table of Contents

Video Upload Options

Confirm