Long-Term Stability Metrics of Photoelectrochemical Water Splitting

Abstract

Photoelectrochemical (PEC) water splitting, one of the most promising technologies for clean hydrogen generation, has drawn considerable attention over the past few decades. Achieving simultaneous highly efficient and stable unassisted PEC water splitting has been the “holy grail” in clean and renewable fuel generation. State-of-the-art photoelectrodes have shown relatively high efficiencies (∼10–20%). Still, their stability is limited due to photoelectrode chemical instability, electrolyte resistance, mass transfer issues, and an often unoptimized experimental setup. In this work, we present a framework and a set of protocols for conducting long-term stability experiments and further provide details on several critical factors such as light source calibration, choosing the right counter electrode, the configuration of the PEC cell, and photoelectrode sample preparation.

Introduction

An essential requirement for large-scale commercialization of PEC water splitting is the device’s durability against harsh electrolytes and under dark and different illumination intensities (Nandjou and Haussener, 2017; Kaneko et al., 2018). Due to the intermittency of solar radiation, the degradation of PEC devices is more accelerated than photovoltaic-electrolyzer devices (Shaner et al., 2016). Most of the high-efficiency semiconductors for PEC like Si (King et al., 2017; Ros et al., 2017) and III-V (Britto et al., 2016) are easily prone to chemical corrosion in the electrolyte (even under dark conditions). Si is easily oxidized to SiO₂ in an aqueous solution (see Eq. 1) and forms a passivation layer on the Si surface, leading to a reduction (Kainthla et al., 1986).

III-V compounds, like GaAs, also go through corrosion reactions (see Eq. 2) due to either accumulation of a large surface hole concentration in the dark or light illumination, generating holes at the surface (Lewerenz, 2014). However, p-type III-arsenide semiconductors have shown remarkable stability under conditions where an As⁰ enriched surface provides passivation against corrosion (Young et al., 2016).

It was observed that N-terminated III-nitride nanostructures show virtually no chemical or photoelectrochemical corrosions when in contact with different electrolytes (Kibria et al., 2016; AlOtaibi et al., 2013; Vanka et al., 2018; Varadhan et al., 2017). Recent studies further revealed that the surfaces of such III-nitride nanostructures could be transformed to oxynitride, which leads to improved PEC performance, instead of degradation, under both one-sun and concentrated sunlight illumination (Zeng et al., 2021). Mi et al. reported one of the longest stability (>3,000 h) using an N-terminated multifunctional GaN nanowire protection scheme on Si photocathode (Vanka et al., 2019) and demonstrated durability under accelerated testing conditions (Zeng et al., 2021). Furthermore, Mi et al. demonstrated high stability of >100 h under a two-electrode experimental setup by utilizing single (STH ∼3%) (Wang et al., 2019) and double junction (STH ∼10%) (Vanka et al., 2020) InGaN/Si photocathodes. The underlying thermodynamic and kinetics of N-terminated (In)GaN nanostructures have been investigated in previous publications (Vanka et al., 2018; Zeng et al., 2021; Vanka et al., 2019; Vanka et al., 2020; He et al., 2019). The basic stability criteria for conduction band minimum and valence band maximum of a photoelectrode include: below and above (Chen and Wang, 2012), where is energy level for cathodic corrosion reaction of semiconductor and is energy level for anodic corrosion reaction of semiconductor (Chen and Wang, 2012). If and fall within the energy bandgap, then the material tends to become corroded or etched under PEC conditions. Furthermore, to avoid the competition of cathodic and anodic photocorrosion with the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, the photoelectrode must satisfy the criteria: above (0 V vs. NHE (Chen and Wang, 2012)) and below [−1.23 V vs. NHE (Chen and Wang, 2012)]. None of the semiconductor materials shown in Figure 1 (Chen and Wang, 2012) satisfy both thermodynamic conditions of stability. In addition to these considerations, excess charge carriers in the photoaborber (mainly metal oxides) will lead to lattice distortions and form localized polarons (Di Valentin and Selloni, 2011; Janotti et al., 2014; Butler et al., 2016). These polarons can inhibit the charge transfer kinetics and affect the interface catalysis process. Thus, electron-hole pair recombination via polarons may hamper the stability of the photoelectrode. Although theoretically PEC water splitting requires 1.23 V, depending on the type of the photoelectrode, co-catalysts, and electrolyte, overpotentials for both hydrogen and oxygen evolution vary, and the redox potential lies typically in the range of 1.4–1.9 V (Chen et al., 2011; Shaner et al., 2016). Application of co-catalysts (e.g., Pt) on the photoelectrode surface provides kinetic protection by directing photogenerated charge carriers towards the favored water-splitting half reactions instead of corrosion reactions (Nandjou and Haussener, 2017). Therefore, the primary role of co-catalysts is to reduce the redox overpotential, facilitate the mass transfer, and efficient charge carrier extraction (Chen et al., 2011; Kaneko et al., 2018).

FIGURE 1

Chen and Wang (2012). Copyright 2012 American Chemical Society.

Over the years, various protection schemes have been employed to enhance the stability of both photocathode and photoanode. The first approach (see Figure 2A) uses relatively thick metal oxide such as TiO₂ (Ros et al., 2017; Yin et al., 2018), Al₂O₃ (Fan et al., 2015), or IrO_x (Mei et al., 2014) as passivation layers for photocathode and photoanode. Even though the stability performance has improved substantially (Ros et al., 2017; Yin et al., 2018), the major issue is photocurrent loss due to poor charge carrier transfer kinetics and light absorption (Kaneko et al., 2018). In addition, these protective layers suffer from the presence of pinholes and often involve the use of additional deposition methods, such as ALD. Henceforth, during stability testing, these pinholes may act as catalytic degradation sites, which eventually leads to exposure of the photoelectrode to the electrolyte solution (Ros et al., 2017; Ben-Naim et al., 2020). Moon et al. observed in their stability experiments a decrease in photocurrent density and photovoltage for TiO₂ protected III-V triple-junction solar cell photocathode (Moon et al., 2020). This performance degradation is due to the pinholes within the TiO₂ layer, which erodes the top junction by allowing acidic electrolyte solution to dissolve the top junction and ultimately lead to delamination (Moon et al., 2020). The second approach (see Figure 2B) is to couple photoelectrode with a highly active catalyst, simultaneously improving stability and maintaining excellent reaction kinetics by efficiently extracting the photogenerated charge carriers (Nandjou and Haussener, 2017). One of the best stabilities achieved for a photocathode (∼60 days) with a relatively low photocurrent was reported by (King et al., 2017) using MoS₂ on Si. Furthermore, high two-electrode stability for GaInAsP/GaAs with MoS₂ protection under 2.6 suns illumination was reported recently (Ben-Naim et al., 2020). Interface losses and device complexity limit the performance of these devices. Although Si photoanode with NiCrO_x/TiO₂ protection (Shaner et al., 2015) showed high stability of ∼2,200 h, the photocurrent density is low, and the applied bias is greater than 1.23 V vs. NHE. Furthermore, hematite (α-Fe₂O₃) and bismuth vanadate (BiVO₄) showed considerable stability (Dias et al., 2016; Kuang et al., 2016). The highest stability for nanostructured BiVO₄ photoanode is >1,000 h using in-situ on-demand NiFe catalyst regeneration (Kuang et al., 2016). The primary issue with the metal-oxides is their low efficiencies because of the limitations in bulk transport of charge carriers and their wide bandgaps (Bae et al., 2017). Another exciting set of stable water splitting electrodes, which have gained attraction over the past decade, is self-healing/self-repairing catalysts. These (photo)electrodes/catalysts (Kanan and Nocera, 2008; Lutterman et al., 2009; Najafpour et al., 2015; Costentin and Nocera, 2017; Feng et al., 2021; Zeng et al., 2021) with the capacity to renew themselves during the water-splitting reaction require special protocols to evaluate the origins of their stability (Zeng et al., 2021). These protocols are beyond the scope of this work.

FIGURE 2

Vanka et al. (2019). Copyright 2019 Royal Society of Chemistry.

An important factor in the stability measurements is the configuration of the PEC cell. As discussed earlier, most of the photoelectrodes are relatively stable in a three-electrode configuration (Vanka et al., 2019), but few devices can reach 100 h under a two-electrode (zero-bias) PEC configuration (Ben-Naim et al., 2020; Vanka et al., 2020). Three-electrode PEC configuration accounts for only the stability of the working photoelectrode ignoring the performance of the counter electrode and the overall PEC system stability (Chen et al., 2011). On the other hand, the two-electrode PEC configuration gives the actual efficiency and durability under a realistic operating environment of the entire PEC cell, including both the working electrode and counter electrode (Hodes, 2012). Thus, it is crucial to perform the stability tests for the photoelectrodes in a two-electrode configuration under AM1.5G one-sun illumination to understand the real stability of the device. While this work focuses on continuous illumination over long durations, understanding PEC system durability under intermittent illumination is also essential for moving this technology from the bench to the field. Henceforth, it is pertinent to develop standard benchmarking stability protocols for the two and three-electrode configurations to permit researchers to evaluate the stability performance of the photoelectrodes against state-of-the-art devices and thereby accelerate the progress of PEC technology for large-scale deployment.

Procedures

Summary of Method

The stability experiments are essential to gain insights into the lifetime of the material. These experiments are conducted by recording the photocurrent against time under continuously applied bias in a two- or three-electrode configuration (Chen et al., 2011). As discussed earlier (see Figure 1), for most materials without protection schemes photocorrosion is thermodynamically favorable compared to HER or OER in an aqueous environment under illumination. The main cause is the accumulation of excess photogenerated charge carriers (holes or electrons), leading to side reactions (such as self-reduction or oxidation) (Su et al., 2017). Therefore, during stability experiments, it is recommended to quantify the evolved H₂ and O₂ to determine FE and STH (Chen et al., 2011). Photocorrosion is indicated by the degradation of photocurrent and/or LSV characteristics (such as onset potential, saturation photocurrent, and fill-factor) with time (Yang et al., 2019). The stability (or CA) experiments are conducted until the failure point, i.e., when the device photocurrent shows a significant drop at a given voltage. As shown in the flowchart (see Figure 3). The stability evaluation of the photoelectrode starts with either CV or LSV scans. These scans reveal whether the photoelectrode has favorable characteristics such as good photocurrent onset voltage, high photocurrent density, and high STH. After determining the photoelectrode photocurrent density vs. voltage (J-V) characteristics, the device’s CA response is measured in an aqueous electrolyte under AM1.5G one sun or concentrated sunlight illumination with no bias (0 V vs. counter electrode) in a two-electrode configuration. The J-V characteristics of the photoelectrode are periodically recorded during the stability experiments to evaluate whether the sample has degraded (reduction in photocurrent density or onset potential). Once the device reaches its catastrophic failure point, physical failure modes observed microscopically, and spectroscopic analysis of chemical transformations can be coupled with electrochemical procedures to inform the degradation mechanism.

FIGURE 3

Bosserez et al. (2015). Copyright 2012 EDP Sciences. (B) H-type glass chamber for PEC H₂ and O₂ evolution.Reprinted (adapted) with permission from Hernández-Pagán et al. (2012). Copyright 2012 Royal Society of Chemistry. (C) Dual compartment PEC cell with SEA, in-, and outlet connection. Reprinted from Bosserez et al. (2015). Copyright 2012 EDP Sciences.

Spectroscopy and electron microscopy provide further insight into the failure mechanism via structural analysis. Using these techniques, we can effectively compare the chemical transformation of the surface morphology before and after the photoelectrochemical reaction, while such chemical transformation either leads to catastrophic degradation or self-healing/self-improving (Kanan and Nocera, 2008; Malara et al., 2016; Toma et al., 2016; Zeng et al., 2021). Either way, the knowledge we obtain through structural analysis will provide feedback for further optimization of our device. Toma et al. (2016) employed EC-AFM to monitor the corrosion of BiVO₄ and provide mechanistic insights into the chemical and photochemical instability of this material, which can be used to guide approaches for further improvement of BiVO₄ photoanode. On the other hand, self-improving via chemical transformation can also be revealed by structural analysis. Zeng et al. (2021) reported that GaN can achieve self-improvement during HER by forming an ultrathin layer of gallium oxynitride, which led to lower overpotential, and higher charge transfer efficiency, and improved durability.

Equipment and Supplies

Electrochemical potentiostat- This is the essential equipment required to conduct J-V, Mott-Schottky, OCP, and CA experiments.

GC- A GC analyzer is required to detect hydrogen and oxygen gas products during PEC reactions. This equipment is also used to determine FE (Chen et al., 2011) and H₂ gas evolution rates.

ICP-MS- ICP-MS is essential to determine any dissolved photoelectrode material, co-catalysts, and other metals/non-metals in electrolyte solution during the reaction (Deutsch et al., 2006).

SEM- This is one of the most used techniques to determine the morphological changes before and after stability experiments, with resolutions in the range of a few nanometers to sub-micrometer scale.

STEM- STEM is essential in analyzing nanometer, or atomic-scale feature sizes by using annular dark-field imaging, spectroscopic mapping by EDX, or EELS.

AFM- AFM scans provide nanometer resolution images of the top surface. For 2D films, AFM is sufficient to understand the surface degradation after stability experiments. However, for 1D nanostructures, this technique may be somewhat limited. Therefore, it is preferred to use SEM or STEM for 1D photoelectrodes. As mentioned earlier, in-situ AFM measurements such as EC-AFM and PC-AFM are instrumental in determining the nanoscale origin of photocurrent (Eichhorn et al., 2018; Nellist et al., 2018; Zeng et al., 2021).

XPS- This technique helps identify the elements, chemical states, and electronic structure of the photoelectrode material.

XRD- XRD scans provide critical information for structural changes of the photoelectrode materials, such as crystal structures, phases, defects, and strain distribution. Therefore, any changes in crystallinity of the material revealed by XRD scans can provide critical information regarding photocorrosion on the surfaces.

Reagents- Alkaline solution (potassium hydroxide, etc.), acid solution (sulfuric acid, etc.), and deionized water.

Instrument or Method Calibration and Standardization

Light source intensity: The light source needs to be regularly recalibrated to maintain 100 mW/cm² power density throughout the stability test (Chen et al., 2011), especially if it is not continuously measured over time.

Electrochemical potentiostat: It is quintessential to calibrate these instruments by following the vendor’s recommendations correctly to obtain reliable and consistent results.

Example of Pt-Decorated GaN/Si Photocathode Stability

Here we explain the three-electrode stability measurements of N-terminated GaN/Si photocathode considering the protocols mentioned earlier.

Step 1: From Figure 4, the first basic step is to calibrate the light source to 100 mW/cm². Mi et al. used Si (bandgap ∼1.1 eV) reference cell to calibrate their light source for GaN/Si photocathode (Vanka et al., 2018).

FIGURE 4

Step 2: From Figures 5A,B, LSV scans show photocurrent onset voltage ∼0.56 V vs. NHE, high saturation photocurrent density ∼37 mA/cm² and ABPE ∼11.9% (at 0.37 V vs. NHE) (Vanka et al., 2018; Vanka et al., 2019). As discussed earlier and shown in Figure 4, using the best sample for stability experiments in terms of high ABPE and excellent LSV characteristics is essential. The morphology of the 1D nanowires with co-catalyst nanoparticles is determined using STEM and SEM techniques (Vanka et al., 2018; Vanka et al., 2019). However, as discussed earlier, the AFM technique may be challenging for analyzing 1D nanowires and catalyst nanoparticles. Figure 5C shows the STEM image of the Pt decorated GaN/Si photocathode before CA experiments.

FIGURE 5

Vanka et al. (2019). Copyright 2019 Royal Society of Chemistry.

Step 3: For the GaN/Si photocathode samples having ABPE >10%, CA experiments are performed in a three-electrode PEC configuration at 0 V vs. NHE in 0.5 M H₂SO₄ under AM 1.5G one sun (Vanka et al., 2018; Vanka et al., 2019). Zeng et al. demonstrated that the photocurrent density of GaN/Si photocathode does not degrade under concentrated sunlight (∼3 suns) illumination for 150 h (Zeng et al., 2021).

Step 4: LSV scans are measured after every run (each run is about 22–24 h duration). As shown in Figure 4, these scans need to be compared with the J-V characteristics before starting the stability experiments to determine whether to proceed further with the CA stability experiments or not (Vanka et al., 2019).

Step 5: The GaN/Si photocathode showed a decrement in photocurrent density, and J-V characteristics changed dramatically after 113 h (Vanka et al., 2018). By performing the structural analysis (STEM and SEM), the root cause of this degradation was attributed to the loss of Pt co-catalyst nanoparticles on the GaN nanowire surface (Vanka et al., 2018). Thus, to maintain the J-V and CA characteristics of GaN/Si photocathode over long periods of stability testing, it is pertinent to regenerate the co-catalyst regularly.

Step 6: Using a new sample (with the same J-V characteristics mentioned in step 2), the experiment is repeated from step 1. In this run, catalyst regeneration is implemented after approximately every 24 h to achieve long-term stability of >3,000 h (Vanka et al., 2019) (see Figure 5D) with no degradation in J-V performance after the experiments (see Figure 5A).

Step 7: The ultra-long stability (CA) experiments for GaN/Si photocathode are stopped after 3,000 h. From Figure 5E, STEM analysis reveals no apparent degradation in GaN nanowire dimensions and fewer Pt co-catalyst nanoparticles on the GaN surface than in Figure 5C (Vanka et al., 2019). Furthermore, ICP-MS (Figure 5F) shows that GaN remains stable throughout the CA experiments. Thus, the structural analysis and theoretical studies reveal that the stability of Pt decorated GaN/Si photocathode is limited by Pt nanoparticles rather than GaN/Si light absorber (Vanka et al., 2018; Vanka et al., 2019; Zeng et al., 2021).

Conclusion

This work provides an overview of the stability requirements of a photoelectrode and the pertinent need to develop standard protocols for long-term stability measurements in a two-electrode and three-electrode configuration. We have illustrated a framework to evaluate the stability of photoelectrode with an optimized experimental setup based on light source calibration, counter electrode optimization, PEC chamber, and sample preparation. The GaN/Si photoelectrode example showed how these protocols lead to proper stability measurements of the device and further improve the performance by understanding the degradation mechanism. We believe that for future stability studies, these benchmarking protocols can serve as valuable guidelines in accelerating the search for new photoelectrodes which can cut the “Gordian knot” of simultaneously achieving ultra-high stability (>10,000 h) and high efficiency (>15%).

References

• 1

  AhmetI. Y.MaY.JangJ.-W.HenschelT.StannowskiB.LopesT.et al (2019). Demonstration of a 50 Cm2 BiVO4 Tandem Photoelectrochemical-Photovoltaic Water Splitting Device. Sustain. Energ. Fuels3 (9), 2366–2379. 10.1039/c9se00246d

  • CrossRef
  • Google Scholar
  • View reference in article

• 2

  AlOtaibiB.NguyenH. P. T.ZhaoS.KibriaM. G.FanS.MiZ. (2013). Highly Stable Photoelectrochemical Water Splitting and Hydrogen Generation Using a Double-Band InGaN/GaN Core/Shell Nanowire Photoanode. Nano Lett.13 (9), 4356–4361. 10.1021/nl402156e

  • CrossRef
  • Google Scholar
  • View reference in article

• 3

  BaeD.SegerB.HansenO.VesborgP. C. K.ChorkendorffI. (2019). Durability Testing of Photoelectrochemical Hydrogen Production under Day/Night Light Cycled Conditions. Chemelectrochem6 (1), 106–109. 10.1002/celc.201800918

  • CrossRef
  • Google Scholar
  • View reference in article

• 4

  BaeD.SegerB.VesborgP. C. K.HansenO.ChorkendorffI. (2017). Strategies for Stable Water Splitting via Protected Photoelectrodes. Chem. Soc. Rev.46 (7), 1933–1954. 10.1039/c6cs00918b

  • CrossRef
  • Google Scholar
  • View reference in article

• 5

  Ben-NaimM.BrittoR. J.AldridgeC. W.MowR.SteinerM. A.NielanderA. C.et al (2020). Addressing the Stability Gap in Photoelectrochemistry: Molybdenum Disulfide Protective Catalysts for Tandem III-V Unassisted Solar Water Splitting. ACS Energ. Lett.5 (8), 2631–2640. 10.1021/acsenergylett.0c01132

  • CrossRef
  • Google Scholar
  • View reference in article

• 6

  BosserezT.RongéJ.van HumbeeckJ.HaussenerS.MartensJ. (2015). Design of Compact Photoelectrochemical Cells for Water Splitting. Oil Gas Sci. Technol. - Rev. IFP Energies Nouvelles70 (5), 877–889. 10.2516/ogst/2015015

  • CrossRef
  • Google Scholar
  • View reference in article

• 7

  BrittoR. J.BenckJ. D.YoungJ. L.HahnC.DeutschT. G.JaramilloT. F. (2016). Molybdenum Disulfide as a Protection Layer and Catalyst for Gallium Indium Phosphide Solar Water Splitting Photocathodes. J. Phys. Chem. Lett.7 (11), 2044–2049. 10.1021/acs.jpclett.6b00563

  • CrossRef
  • Google Scholar
  • View reference in article

• 8

  ButlerK. T.DringoliB. J.ZhouL.RaoP. M.WalshA.TitovaL. V. (2016). Ultrafast Carrier Dynamics in BiVO4 Thin Film Photoanode Material: Interplay between Free Carriers, Trapped Carriers and Low-Frequency Lattice Vibrations. J. Mater. Chem. A.4 (47), 18516–18523. 10.1039/c6ta07177e

  • CrossRef
  • Google Scholar
  • View reference in article

• 9

  ChenS.WangL.-W. (2012). Thermodynamic Oxidation and Reduction Potentials of Photocatalytic Semiconductors in Aqueous Solution. Chem. Mater.24 (18), 3659–3666. 10.1021/cm302533s

  • CrossRef
  • Google Scholar
  • View reference in article

• 10

  ChenZ.JaramilloT. F.DeutschT. G.Kleiman-ShwarscteinA.FormanA. J.GaillardN.et al (2011). Accelerating Materials Development for Photoelectrochemical Hydrogen Production: Standards for Methods, Definitions, and Reporting Protocols. J. Mater. Res.25 (01), 3–16. 10.1557/jmr.2010.0020

  • CrossRef
  • Google Scholar
  • View reference in article

• 11

  ChoiM. J.JungJ.-Y.ParkM.-J.SongJ.-W.LeeJ.-H.BangJ. H. (2014). Long-term Durable Silicon Photocathode Protected by a Thin Al2O3/SiOx Layer for Photoelectrochemical Hydrogen Evolution. J. Mater. Chem. A.2 (9), 2928. 10.1039/c3ta14443g

  • CrossRef
  • Google Scholar
  • View reference in article

• 12

  CostentinC.NoceraD. G. (2017). Self-healing Catalysis in Water. Proc. Natl. Acad. Sci. U.S.A.114 (51), 13380–13384. 10.1073/pnas.1711836114

  • CrossRef
  • Google Scholar
  • View reference in article

• 13

  DeutschT. G.KovalC. A.TurnerJ. A. (2006). III−V Nitride Epilayers for Photoelectrochemical Water Splitting: GaPN and GaAsPN. J. Phys. Chem. B110 (50), 25297–25307. 10.1021/jp0652805

  • CrossRef
  • Google Scholar
  • View reference in article

• 14

  Di ValentinC.SelloniA. (2011). Bulk and Surface Polarons in Photoexcited Anatase TiO2. J. Phys. Chem. Lett.2 (17), 2223–2228. 10.1021/jz2009874

  • CrossRef
  • Google Scholar
  • View reference in article

• 15

  DiasP.VilanovaA.LopesT.AndradeL.MendesA. (2016). Extremely Stable Bare Hematite Photoanode for Solar Water Splitting. Nano Energy23, 70–79. 10.1016/j.nanoen.2016.03.008

  • CrossRef
  • Google Scholar
  • View reference in article

• 16

  EichhornJ.KastlC.CooperJ. K.ZieglerD.SchwartzbergA. M.SharpI. D.et al (2018). Nanoscale Imaging of Charge Carrier Transport in Water Splitting Photoanodes. Nat. Commun.9 (1), 2597. 10.1038/s41467-018-04856-8

  • CrossRef
  • Google Scholar
  • View reference in article

• 17

  FanR.DongW.FangL.ZhengF.SuX.ZouS.et al (2015). Stable and Efficient Multi-Crystalline N+p Silicon Photocathode for H2 Production with Pyramid-like Surface Nanostructure and Thin Al2O3 Protective Layer. Appl. Phys. Lett.106 (1), 013902. 10.1063/1.4905511

  • CrossRef
  • Google Scholar
  • View reference in article

• 18

  FengC.WangF.LiuZ.NakabayashiM.XiaoY.ZengQ.et al (2021). A Self-Healing Catalyst for Electrocatalytic and Photoelectrochemical Oxygen Evolution in Highly Alkaline Conditions. Nat. Commun.12 (1), 5980. 10.1038/s41467-021-26281-0

  • CrossRef
  • Google Scholar
  • View reference in article

• 19

  HagfeldtA.LindströmH.SödergrenS.LindquistS.-E. (1995). Photoelectrochemical Studies of Colloidal TiO₂ Films: The Effect of Oxygen Studied by Photocurrent Transients. J. Electroanalytical Chem.381 (1), 39–46. 10.1016/0022-0728(94)03622-a

  • CrossRef
  • Google Scholar
  • View reference in article

• 20

  HeY.VankaS.GaoT.HeD.EspanoJ.ZhaoY.et al (2019). Dependence of Interface Energetics and Kinetics on Catalyst Loading in a Photoelectrochemical System. Nano Res.12, 2378–2384. 10.1007/s12274-019-2346-3

  • CrossRef
  • Google Scholar
  • View reference in article

• 21

  Hernández-PagánE. A.Vargas-BarbosaN. M.WangT.ZhaoY.SmotkinE. S.MalloukT. E. (2012). Resistance and Polarization Losses in Aqueous Buffer–Membrane Electrolytes for Water-Splitting Photoelectrochemical Cells. Energ. Environ. Sci.5 (6), 7582. 10.1039/C2EE03422K

  • CrossRef
  • Google Scholar
  • View reference in article

• 22

  HodesG. (2012). Photoelectrochemical Cell Measurements: Getting the Basics Right. J. Phys. Chem. Lett.3 (9), 1208–1213. 10.1021/jz300220b

  • CrossRef
  • Google Scholar
  • View reference in article

• 23

  JanottiA.VarleyJ. B.ChoiM.Van de WalleC. G. (2014). Vacancies and Small Polarons in SrTiO₃. Phys. Rev. B90 (8), 085202. 10.1103/physrevb.90.085202

  • CrossRef
  • Google Scholar
  • View reference in article

• 24

  KainthlaR. C.ZelenayB.BockrisJ. O. M. (1986). Protection of n‐Si Photoanode against Photocorrosion in Photoelectrochemical Cell for Water Electrolysis. J. Electrochem. Soc.133 (2), 248–253. 10.1149/1.2108556

  • CrossRef
  • Google Scholar
  • View reference in article

• 25

  KananM. W.NoceraD. G. (2008). In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co 2+. Science321 (5892), 1072–1075. 10.1126/science.1162018

  • CrossRef
  • Google Scholar
  • View reference in article

• 26

  KanekoH.MinegishiT.DomenK. (2018). Recent Progress in the Surface Modification of Photoelectrodes toward Efficient and Stable Overall Water Splitting. Chem. Eur. J.24 (22), 5697–5706. 10.1002/chem.201703104

  • CrossRef
  • Google Scholar
  • View reference in article

• 27

  KibriaM. G.QiaoR.YangW.BoukahilI.KongX.ChowdhuryF. A.et al (2016). Atomic-Scale Origin of Long-Term Stability and High Performance Ofp-GaN Nanowire Arrays for Photocatalytic Overall Pure Water Splitting. Adv. Mater.28 (38), 8388–8397. 10.1002/adma.201602274

  • CrossRef
  • Google Scholar
  • View reference in article

• 28

  KingL. A.HellsternT. R.ParkJ.SinclairR.JaramilloT. F. (2017). Highly Stable Molybdenum Disulfide Protected Silicon Photocathodes for Photoelectrochemical Water Splitting. ACS Appl. Mater. Inter.9 (42), 36792–36798. 10.1021/acsami.7b10749

  • CrossRef
  • Google Scholar
  • View reference in article

• 29

  KuangY.JiaQ.MaG.HisatomiT.MinegishiT.NishiyamaH.et al (2016). Ultrastable Low-Bias Water Splitting Photoanodes via Photocorrosion Inhibition and In Situ Catalyst Regeneration. Nat. Energ.2 (1), 16191. 10.1038/nenergy.2016.191

  • CrossRef
  • Google Scholar
  • View reference in article

• 30

  LewerenzH. J. (2014). Semiconductor Surface Transformations for Photoelectrochemical Energy Conversion. J. Electrochem. Soc.161 (13), H3117–H3129. 10.1149/2.0211413jes

  • CrossRef
  • Google Scholar
  • View reference in article

• 31

  LuttermanD. A.SurendranathY.NoceraD. G. (2009). A Self-Healing Oxygen-Evolving Catalyst. J. Am. Chem. Soc.131 (11), 3838–3839. 10.1021/ja900023k

  • CrossRef
  • Google Scholar
  • View reference in article

• 32

  MalaraF.FabbriF.MarelliM.NaldoniA. (2016). Controlling the Surface Energetics and Kinetics of Hematite Photoanodes through Few Atomic Layers of NiOx. ACS Catal.6 (6), 3619–3628. 10.1021/acscatal.6b00569

  • CrossRef
  • Google Scholar
  • View reference in article

• 33

  MeiB.SegerB.PedersenT.MaliziaM.HansenO.ChorkendorffI.et al (2014). Protection of P+-N-Si Photoanodes by Sputter-Deposited Ir/IrOx Thin Films. J. Phys. Chem. Lett.5 (11), 1948–1952. 10.1021/jz500865g

  • CrossRef
  • Google Scholar
  • View reference in article

• 34

  MoonC.SegerB.VesborgP. C. K.HansenO.ChorkendorffI. (2020). Wireless Photoelectrochemical Water Splitting Using Triple-Junction Solar Cell Protected by TiO2. Cel Rep. Phys. Sci.1 (12), 100261. 10.1016/j.xcrp.2020.100261

  • CrossRef
  • Google Scholar
  • View reference in article

• 35

  NajafpourM. M.FeketeM.SedighD. J.AroE.-M.CarpentierR.Eaton-RyeJ. J.et al (2015). Damage Management in Water-Oxidizing Catalysts: From Photosystem II to Nanosized Metal Oxides. ACS Catal.5 (3), 1499–1512. 10.1021/cs5015157

  • CrossRef
  • Google Scholar
  • View reference in article

• 36

  NandjouF.HaussenerS. (2017). Degradation in Photoelectrochemical Devices: Review with an Illustrative Case Study. J. Phys. D: Appl. Phys.50 (12), 124002. 10.1088/1361-6463/aa5b11

  • CrossRef
  • Google Scholar
  • View reference in article

• 37

  NellistM. R.QiuJ.LaskowskiF. A. L.TomaF. M.BoettcherS. W. (2018). Potential-Sensing Electrochemical AFM Shows CoPi as a Hole Collector and Oxygen Evolution Catalyst on BiVO4 Water-Splitting Photoanodes. ACS Energ. Lett.3 (9), 2286–2291. 10.1021/acsenergylett.8b01150

  • CrossRef
  • Google Scholar
  • View reference in article

• 38

  ObataK.van de KrolR.SchwarzeM.SchomäckerR.AbdiF. F. (2020). In Situ observation of pH Change during Water Splitting in Neutral pH Conditions: Impact of Natural Convection Driven by Buoyancy Effects. Energy Environ. Sci.13 (12), 5104–5116. 10.1039/d0ee01760d

  • CrossRef
  • Google Scholar
  • View reference in article

• 39

  RosC.AndreuT.Hernandez-AlonsoM. D.Penelas-PerezG.ArbiolJ.MoranteJ. R. (2017). Charge Transfer Characterization of ALD-Grown TiO₂ Protective Layers in Silicon Photocathodes. ACS Appl. Mater. Inter.9 (21), 17932–17941. 10.1021/acsami.7b02996

  • CrossRef
  • Google Scholar
  • View reference in article

• 40

  ShanerM. R.AtwaterH. A.LewisN. S.McFarlandE. W. (2016). A Comparative Technoeconomic Analysis of Renewable Hydrogen Production Using Solar Energy. Energ. Environ. Sci.9 (7), 2354–2371. 10.1039/c5ee02573g

  • CrossRef
  • Google Scholar
  • View reference in article

• 41

  ShanerM. R.HuS.SunK.LewisN. S. (2015). Stabilization of Si Microwire Arrays for Solar-Driven H2O Oxidation to O2(g) in 1.0 M KOH(aq) Using Conformal Coatings of Amorphous TiO2. Energ. Environ. Sci.8 (1), 203–207. 10.1039/c4ee03012e

  • CrossRef
  • Google Scholar
  • View reference in article

• 42

  ShinagawaT.TakanabeK. (2015). Electrocatalytic Hydrogen Evolution under Densely Buffered Neutral pH Conditions. J. Phys. Chem. C119 (35), 20453–20458. 10.1021/acs.jpcc.5b05295

  • CrossRef
  • Google Scholar
  • View reference in article

• 43

  ShinagawaT.TakanabeK. (2016). Electrolyte Engineering toward Efficient Hydrogen Production Electrocatalysis with Oxygen-Crossover Regulation under Densely Buffered Near-Neutral pH Conditions. J. Phys. Chem. C120 (3), 1785–1794. 10.1021/acs.jpcc.5b12137

  • CrossRef
  • Google Scholar
  • View reference in article

• 44

  ShinagawaT.TakanabeK. (2015). Identification of Intrinsic Catalytic Activity for Electrochemical Reduction of Water Molecules to Generate Hydrogen. Phys. Chem. Chem. Phys.17 (23), 15111–15114. 10.1039/c5cp02330k

  • CrossRef
  • Google Scholar
  • View reference in article

• 45

  SuJ.WeiY.VayssieresL. (2017). Stability and Performance of Sulfide-, Nitride-, and Phosphide-Based Electrodes for Photocatalytic Solar Water Splitting. J. Phys. Chem. Lett.8 (20), 5228–5238. 10.1021/acs.jpclett.7b00772

  • CrossRef
  • Google Scholar
  • View reference in article

• 46

  TomaF. M.CooperJ. K.KunzelmannV.McDowellM. T.YuJ.LarsonD. M.et al (2016). Mechanistic Insights into Chemical and Photochemical Transformations of Bismuth Vanadate Photoanodes. Nat. Commun.7, 12012. 10.1038/ncomms12012

  • CrossRef
  • Google Scholar
  • View reference in article

• 47

  VankaS.ArcaE.ChengS.SunK.BottonG. A.TeeterG.et al (2018). High Efficiency Si Photocathode Protected by Multifunctional GaN Nanostructures. Nano Lett.18 (10), 6530–6537. 10.1021/acs.nanolett.8b03087

  • CrossRef
  • Google Scholar
  • View reference in article

• 48

  VankaS.SunK.ZengG.PhamT. A.TomaF. M.OgitsuT.et al (2019). Long-term Stability Studies of a Semiconductor Photoelectrode in Three-Electrode Configuration. J. Mater. Chem. A.7, 27612–27619. 10.1039/c9ta09926c

  • CrossRef
  • Google Scholar
  • View reference in article

• 49

  VankaS.ZhouB.AwniR. A.SongZ.ChowdhuryF. A.LiuX.et al (2020). InGaN/Si Double-Junction Photocathode for Unassisted Solar Water Splitting. ACS Energ. Lett.5 (12), 3741–3751. 10.1021/acsenergylett.0c01583

  • CrossRef
  • Google Scholar
  • View reference in article

• 50

  VaradhanP.FuH.-C.PrianteD.RetamalJ. R. D.ZhaoC.EbaidM.et al (2017). Surface Passivation of GaN Nanowires for Enhanced Photoelectrochemical Water-Splitting. Nano Lett.17 (3), 1520–1528. 10.1021/acs.nanolett.6b04559

  • CrossRef
  • Google Scholar
  • View reference in article

• 51

  WangY.WuY.SchwartzJ.SungS. H.HovdenR.MiZ. (2019). A Single-Junction Cathodic Approach for Stable Unassisted Solar Water Splitting. Joule3 (10), 2444–2456. 10.1016/j.joule.2019.07.022

  • CrossRef
  • Google Scholar
  • View reference in article

• 52

  YangW.PrabhakarR. R.TanJ.TilleyS. D.MoonJ. (2019). Strategies for Enhancing the Photocurrent, Photovoltage, and Stability of Photoelectrodes for Photoelectrochemical Water Splitting. Chem. Soc. Rev.48 (19), 4979–5015. 10.1039/c8cs00997j

  • CrossRef
  • Google Scholar
  • View reference in article

• 53

  YinZ.FanR.HuangG.ShenM. (2018). 11.5% Efficiency of TiO2 Protected and Pt Catalyzed N+np+-Si Photocathodes for Photoelectrochemical Water Splitting: Manipulating the Pt Distribution and Pt/Si Contact. Chem. Commun.54 (5), 543–546. 10.1039/c7cc08409a

  • CrossRef
  • Google Scholar
  • View reference in article

• 54

  YoungJ. L.SteirerK. X.DzaraM. J.TurnerJ. A.DeutschT. G. (2016). Remarkable Stability of Unmodified GaAs Photocathodes during Hydrogen Evolution in Acidic Electrolyte. J. Mater. Chem. A.4 (8), 2831–2836. 10.1039/c5ta07648j

  • CrossRef
  • Google Scholar
  • View reference in article

• 55

  ZengG.PhamT. A.VankaS.LiuG.SongC.CooperJ. K.et al (2021). Development of a Photoelectrochemically Self-Improving Si/GaN Photocathode for Efficient and Durable H2 Production. Nat. Mater.20, 1130–1135. 10.1038/s41563-021-00965-w

  • CrossRef
  • Google Scholar
  • View reference in article