Metal Cocatalysts Research Articles

Theoretical Understanding of LaTaON2 Decorated With Metal Cocatalysts for Photocatalytic Hydrogen Evolution Reaction

ABSTRACTLaTaON2 is a promising visible‐light‐responsive photocatalyst for water splitting because of its broad visible light absorption and suitable band edge positions. However, the high defect concentration hinders the charge transfer and results in the poor photocatalytic performance of LaTaON2. Loading proper cocatalysts is one of the most efficient strategies for promoting charge separation/transfer and achieving high reaction activity. In this work, we have used density functional theory calculations to study the depositions of Pt, Ru, and Ni single atom cocatalysts on LaTaON2(010) surface. The most stable adsorption configuration is the same site for all the elements, namely the top of the N atom on the La‐terminated surface and the fourfold hollow site on the Ta‐terminated surface. The adsorption of the metal single atom on Ta‐termination is stronger than that on La‐termination due to the formation of more bonds. Upon the deposition, no localized impurity states appear in the middle of the forbidden gap since the nd states of metal adatoms are located within the valence band and conduction band of LaTaON2. The efficiency of the photocatalysts is probed by investigating their ability to adsorb the H atom in a thermodynamically favorable manner. Our results reveal that the energetically favorable sites of HER are the N atom on the La‐termination and the O and N atoms on the Ta‐termination, respectively. Compared with the clean surface, the surfaces with Pt, Ru, and Ni single adatoms exhibit higher performance for HER because loading metal cocatalysts can further activate the surface nonmetal atoms and reduce the Gibbs free energy of hydrogen adsorption. The work gives an atom‐level insight into the role of metal single atom cocatalysts in the LaTaON2 photocatalyst for hydrogen production.

Exploring Metal- and Porphyrin-Modified TiO2-Based Photocatalysts for Efficient and Sustainable Hydrogen Production

Photocatalytic H2 production is one of the most promising approaches for sustainable energy. The literature presents a plethora of carefully designed systems aimed at harnessing solar energy and converting it into chemical energy. However, the main drawback of the reported photocatalysts is their stability. Thus, the development of a cost-effective and stable photocatalyst, suitable for real-world applications remains a challenge. An ideal photocatalyst for H2 production must possess appropriate band-edge energy positions, an effective sacrificial agent, and a suitable cocatalyst. Among the various photocatalysts studied, TiO2 stands out due to its stability, abundance, and non-toxicity. However, its efficiency in the visible spectrum is limited by its wide bandgap. Metal doping is an effective strategy to enhance electron–hole separation and improve light absorption efficiency, thereby boosting H2 synthesis. Common metal cocatalysts used as TiO2 dopants include platinum (Pt), gold (Au), copper (Cu), nickel (Ni), cobalt (Co), ruthenium (Ru), iron (Fe), and silver (Ag), as well as bimetallic combinations such as Ni-Fe, Ni-Cu, Nb-Ta, and Ni-Pt. In all cases, doped TiO2 exhibits higher H2 production performance compared to undoped TiO2, as metals provide additional reaction sites and enhance charge separation. The use of bimetallic dopants further optimizes the hydrogen evolution reaction. Additionally, porphyrins, with their strong visible light absorption and efficient electron transfer properties, have demonstrated potential in TiO2 photocatalysis. Their incorporation expands the photocatalyst’s light absorption range into the visible spectrum, enhancing H2 production efficiency. This review paper explores the principles and advancements in metal- and porphyrin-doped TiO2 photocatalysts, highlighting their potential for sustainable hydrogen production.

Covalent organic framework without cocatalyst loading for efficient photocatalytic sacrificial hydrogen production from water

Metals are typically essential as either integral components within photocatalysts or as cocatalyst modifiers to enable efficient artificial photosynthesis, such as water splitting and carbon dioxide reduction. However, developing photocatalysts that function effectively without metal cocatalysts remains challenging due to their cost and scarcity. Here we show a nonstoichiometric β-ketoenamine-linked covalent organic framework that operates without cocatalysts, achieving hydrogen production rates of 15.48 mmol·g⁻¹·h⁻¹ from seawater and 22.45 mmol·g⁻¹·h⁻¹ from water with an ascorbic acid scavenger under visible light. It outperforms many reported platinum-modified covalent organic frameworks and metal-containing inorganic photocatalysts. The enhanced performance is attributed to its broad light absorption edge extending to approximately 660 nm, efficient charge separation, and the presence of abundant active oxygen sites derived from carbonyl groups, which exhibit a low hydrogen-binding Gibbs free energy change. This work lays the groundwork for designing cost-effective photocatalytic systems suitable for large-scale hydrogen production.

In Situ Reinforced g-C3N4/CoO/CoP Ternary Composite for Enhanced Photocatalytic H2 Production

To meet the growing demand for renewable energy, developing efficient and cost-effective photocatalytic materials is crucial. Specifically, designing photocatalysts with high charge separation efficiency and abundant hydrogen production active sites remains a key challenge for practical applications. In this study, a carbon nitride (g-C3N4)-based ternary photocatalyst has been constructed for enhanced photocatalytic H2 production without the need for precious metal cocatalysts. CoO nanoparticles were loaded onto the surface of g-C3N4 via in situ thermal decomposition. Subsequently, a series of g-C3N4/CoO/CoP ternary composites were successfully prepared using a direct one-step phosphorization method. Under optimized conditions, the g-C3N4/CoO/CoP catalyst exhibits a hydrogen evolution activity of 1277.9 μmol·g−1·h−1, which is 4 times higher than that of g-C3N4/CoO (with g-C3N4 alone showing no hydrogen evolution activity). Its performance is comparable to that of the commonly used Pt cocatalyst. The performance improvement may be attributed to the tight bonding of N-P bonds, which effectively promotes the transport of photogenerated carriers, while the increased loading of CoP provides more active sites. The results offer a promising strategy for designing efficient and low-cost photocatalytic materials.

Critical impacts of metal cocatalysts on oxidation kinetics and optimal reaction conditions of photocatalytic methane reforming.

Metal cocatalysts in photocatalysis are typically regarded as promoting only the reduction reactions. Here, we demonstrate that photocatalytic oxidation kinetics and optimal pressure of methane vary significantly with the loading amount of metal cocatalysts. These variations are well described by kinetic analyses treating molecular-level congestion of oxidation intermediates.

A Metal‐Free Boron Carbon Nitride (BCN) Photocatalyst for Enhanced CO2‐to‐CH4 Conversion by Surface Electronic Tuning

Graphitic carbon nitride (g‐C3N4) has emerged as an attractive metal‐free photocatalyst due to its numerous advantages like tunable surface chemistry, Earth abundance, and nontoxicity. Unfortunately, its photocatalytic efficiency has been seriously limited by charge carrier recombination and low reaction dynamics. Here, we report a metal‐free BCN photocatalyst achieving highly selective CO2‐to‐CH4 conversion under visible light without requiring any metal cocatalyst. The exfoliated CN nanosheets can enrich the reaction interface with protons to accelerate the protonation of CO intermediate to further produce CH4. Moreover, B doping not only introduces more reactive defects but also tunes its electronic structure with a more negative conduction band for rapid electron extraction and enhance CO2‐to‐CH4 conversion. Photocatalytic measurements show that CH4 production rate and CH4/CO ratio are 24 and 13 times higher than those of bulk CN, respectively. The CH4 production rate can also reach 130 and 31 times higher than that of few‐layer g‐C3N4 (FL‐CN) and Cu/FL‐CN, respectively. The electron selectivity toward CH4 generation on BCN photocatalysts can reach ≈90%. Furthermore, sunlight driving CO2‐to‐CH4 conversion on such BCN photocatalysts has also been demonstrated. This work offers new insights for the design of customized multifunctional 2D materials for solar‐driven CO2 conversion to CH4.

Electron Transfer Energetics in Photoelectrochemical CO2 Reduction at Viologen Redox Polymer-Modified p-Si Electrodes.

While redox polymer-mediated catalysis at silicon photoelectrodes has been studied since the 1980s, there have been few detailed studies of these materials in photoelectrochemical CO2 reduction. Here, we develop silicon photoelectrodes functionalized with a viologen-based polymer that mediates the formation of catalytic gold nanoparticles. The presence of gold was confirmed by X-ray photoelectron spectroscopy (XPS), and the nanoparticles were imaged with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). We probed the CO2 reduction process during bulk photoelectrolysis to find modest, yet consistent CO faradaic efficiencies across a range of applied potentials. Operando surface-enhanced Raman spectroscopy (SERS) was used to measure the Fermi levels of both the viologen polymer and the Au catalyst sites. The operando measurement of the Fermi levels of all three components of the photocathode provides a unified picture of the electron transfer process in the semiconductor-redox polymer-catalyst system. The redox polymer serves as the electron transfer mediator between the Si substrate and Au sites. In addition, the Au Fermi level equilibrates with the Fermi level of the viologen polymer, which in turn fixes the quasi-Fermi level of Au catalysts at the p-Si/redox polymer interface. This suggests a potential future direction of using redox polymers with tunable potentials to modulate the potential of metal cocatalysts and thus control the reaction selectivity.

NiB as a Non-noble Metal Cocatalyst Electronic Bridge to Enhance the Photocatalytic Hydrogen Production of Cd3(C3N3S3)2

NiB as a Non-noble Metal Cocatalyst Electronic Bridge to Enhance the Photocatalytic Hydrogen Production of Cd3(C3N3S3)2

Highly Defined Layered 2D Sulfur Nanosheets from 0D Sulfur Dots and their use in the Photocatalytic Oxidative Coupling of Aryl Amines to Aromatic Azo Compounds.

A highly defined multi-layered 2D sulphur nanosheets have been prepared from 0D sulphur dots by hydrothermal based growth process. Slow transformation of sulphur dots to sulphur sheets allow reorganization of elemental sulphur and sulphur containing functional groups, resulting higher crystallinity in sulphur nanosheets with respect to sulphur dots. It is further correlated with the detailed photophysical studies. Low temperature photoluminescence spectra confirm that the exciton binding energy of 2D sulphur sheets are lower than 0D sulphur dots. The exciton-phonon coupling is also higher in sulphur sheet with respect to sulphur dots. Overall, the photoinduced charge separation process improves throughout the highly defined 2D matrix of sulphur sheets. It is further supported by electrochemical impedance spectroscopy and transient photocurrent studies. Finally, both sulphur dots and sulphur sheets have been used for photocatalytic azo bond formation where both photoinduced electrons and holes have been utilized simultaneously. Results suggest almost 3 folds enhancement in catalytic efficiency for sulphur sheets with respect to sulphur dots without any metal co-catalyst. Controlled experiments suggest that the azo bond formation happens through complete photocatalysis process. Detailed mechanism has been proved by identifying the intermediates and free radicals through photo-responsive EPR studies and various chemical scavenging experiments.

Synergistic Metal-Support Interactions in Au/GaN Catalysts for Photoelectrochemical Nitrate Reduction to Ammonia.

Metal-support interactions are crucial in the electrochemical synthesis of ammonia (NH3) from nitrate (NO3 -) reduction reaction, enabling efficient NH3 production under mild conditions. However, the complexity of the reaction pathways often limits efficiency. Here, a photoelectrochemical system composed of gold (Au) nanoclusters supported on gallium nitride (GaN) nanowires is introduced, grown on a n+-p Si wafer, for selective reduction of NO3 - to NH3 under solar illumination. NO3 - ions are preferentially adsorbed and reduced to nitrite (NO2 -) on the GaN nanowires, which then transfer to adjacent Au nanoclusters to complete the NH3 synthesis. This mechanism is confirmed by both experimental data and theoretical calculations. Optimizing the surface coverage and size of Au nanoclusters on the GaN nanowires significantly enhanced catalytic activity compared to that on planar n+-p Si photoelectrodes, achieving a faradaic efficiency of 91.8% at -0.4 VRHE and a high NH3 production rate of 131.1µmolcm-2h-1 at -0.8 VRHE. These findings highlight the synergetic effect between metal co-catalysts and semiconductor supports in designing photoelectrodes for multi-step NO3 - reduction.

Role of Metal Cocatalysts in the Photocatalytic Production of Hydrogen from Water Revisited.

The use of photocatalysts to promote the production of molecular hydrogen from water, following the so-called water splitting reaction, continues to be a promising route for the green production of fuels. The molecular basis of this photocatalysis is the photoexcitation of electrons from the valence band of semiconductors to their conduction band, from which they can be transferred to chemical reactants, protons in the case of water, to promote a reduction reaction. The mechanism by which such a process takes place has been studied extensively using titanium oxide, a simple material that fulfills most requirements for water splitting. However, photocatalysis with TiO2 tends to be highly inefficient; a cocatalyst, commonly a late transition metal (Au, Pt) in nanoparticle form, needs to be added to facilitate the production of H2. The metal is widely believed to help with the scavenging of the excited electrons from the conduction band of the semiconductor in order to prevent their recombination with the accompanying hole formed in the valence band, a step that cancels the initial photon absorption and competes with the photolytic chemical reduction. Here we review and analyze the molecular basis for that mechanism and argue for an alternative explanation, that the role of the metal is to help with the recombination of the atomic hydrogen atoms produced by proton reduction on the semiconductor surface instead. First, we summarize what is known about the electronic structure of these photocatalysts and how the electronic levels need to line up for the reduction of protons in water to be feasible. Next, we review the current understanding of the dynamics of the steps associated with the absorption of photons, the de-excitation via electron-hole pair recombination and fluorescence decay, and the electronic transitions that lead to proton reduction, and contrast those with the rates of the chemical steps required to produce molecular hydrogen. The following section addresses the changes introduced by the addition of the metal cocatalyst, comparatively evaluating its role as either an electron scavenger or a promoter of the recombination of hydrogen atoms. A discussion of the viable chemical mechanisms for the latter pathway is included. Finally, we briefly mention other associated aspects of this photocatalysis, including the possible promotion of H2 production with visible light via resonant excitation of the surface plasmon of Au nanoparticles, the use of single-metal (Au, Pt) atom catalysts and of yolk-shell nanostructures, and the reduction of organic molecules. We end with a brief personal perspective on the possible generality of the concepts introduced in this Critical Review.

Unlocking the Key to Photocatalytic Hydrogen Production Using Electronic Mediators for Z-Scheme Water Splitting.

A prevalent challenge in particulate photocatalytic water splitting lies in the fact that while numerous photocatalysts exhibit outstanding hydrogen evolution reaction (HER) activity in organic sacrificial reagents, their performance diminishes markedly in a Z-scheme water splitting system using electronic mediators. This underlying reason remains undefined, posing a long-standing issue in photocatalytic water splitting. Herein, we unveiled that the primary reason for the decreased HER activity in electronic mediators is due to the strong adsorption of shuttle ions on cocatalyst surfaces, which inhibits the initial proton reduction and results in a severe backward reaction of the oxidized shuttle ions. To address this, taking typical visible-light-responsive photocatalysts, BaTaO2N and SrTiO3:Rh, as examples, we have developed a strategy via selective surface modification of metal cocatalysts (such as Pt, Ru) with chromium oxide species (CrOx) to prevent the adsorption of shuttle ions. It is demonstrated that the photocatalytic HER activities of BaTaO2N and SrTiO3:Rh can be improved by one to two orders of magnitude in diverse shuttle ions. The introduced CrOx substantially weakens the interaction between the metal cocatalysts and shuttle ions, promotes proton adsorption for the HER reaction, and also suppresses the backward reaction between shuttle ions. Owing to the improved HER activity, the photocatalytic performance of Z-scheme water splitting is significantly enhanced, providing a feasible strategy for constructing efficient Z-scheme systems in heterogeneous photocatalysis.

A Theoretical Investigation on the Mechanism of CO2 Reduction Reaction over NaTaO3 photocatalyst Modified with Metal Cocatalysts

The photocatalytic conversion of CO2 into useful chemicals and fuels is a promising approach for storing solar energy and solving the global environmental issues. Getting insight into its reaction mechanism...

Electronic structure engineering and a cascade electron transfer channel in a Ni2P/1T-WS2/ZnIn2S4 ternary heterojunction for enhanced photocatalytic hydrogen evolution: construction, kinetics, and mechanistic insights

The positive synergies between the metallic 1T-WS2 and Ni2P dual cocatalysts in electronic structure engineering and charge transfer kinetics greatly contribute to the significantly enhanced H2 evolution performance of the ZnIn2S4 catalyst.

Photoelectrochemical CO2 reduction on CuO-Cu2O nanocomposites with noble metal co-catalysts enhances the production of C1 oxygenates and acetate

Photoelectrochemical CO2 reduction on CuO-Cu2O nanocomposites with noble metal co-catalysts enhances the production of C1 oxygenates and acetate

Photogenerated charge carrier dynamics on Pt-loaded SrTiO3 nanoparticles studied via transient-absorption spectroscopy.

Loading cocatalysts on semiconductor-based photocatalysts to create active reaction sites is a preferable method to enhance photocatalytic activity and a widely adopted strategy to achieve effective photocatalytic applications. Although theoretical calculations suggest that the broad density of states of noble metal cocatalysts, such as Pt, act as a recombination center, this has never been experimentally demonstrated. Herein, we employed pico-nano and nano-micro second transient absorption spectroscopy to investigate the often overlooked photogenerated holes, instead of the widely studied electrons on Pt- and Ni-loaded SrTiO3 to evaluate the effects of cocatalysts as a recombination center. It is demonstrated that Pt serves as the recombination center with no sacrificial agent; recombination can be suppressed by a hole scavenger, while recombination is not significant on Ni with localized density of states. It is also found that photo-generated holes in SrTiO3 tend to migrate to Pt within 400 ps, and photo-generated holes generated in the bulk gradually migrate to Pt cocatalysts in a micro-second regime.

Toward Spatial Control of Reaction Selectivity on Photocatalysts Using Area-Selective Atomic Layer Deposition on the Model Dual Site Electrocatalyst Platform.

Photocatalytic water splitting is a promising route to low-cost, green H2. However, this approach is currently limited in its solar-to-hydrogen conversion efficiency. One major source of efficiency loss is attributed to the high rates of undesired side and back reactions, which are exacerbated by the proximity of neighboring oxidation and reduction sites. Nanoscopic oxide coatings have previously been used to selectively block undesired reactants from reaching active sites; however, a coating encapsulating the entire photocatalyst particle limits activity as it cannot facilitate both half-reactions. In this work, area selective atomic layer deposition (AS-ALD) was used to selectively deposit semipermeable TiO2 films onto model metallic cocatalysts for enhancing reaction selectivity while maintaining a high overall activity. Pt and Au were used as exemplary reduction and oxidation cocatalyst sites, respectively, where Au was deactivated toward ALD growth through self-assembled thiol monolayers while TiO2 was coated onto Pt sites. Electroanalytical measurements of monometallic thin film electrodes showed that the TiO2-encapsulated Pt effectively suppressed undesired H2 oxidation and Fe(II)/Fe(III) redox reactions while still permitting the desired hydrogen evolution reaction (HER). A planar model photocatalyst platform containing patterned interdigitated arrays of Au and Pt microelectrodes was further assessed using scanning electrochemical microscopy (SECM), demonstrating the successful use of AS-ALD to enable local reaction selectivity in a dual-reaction-site (photo)electrocatalytic system. Finally, interdigitated microelectrodes having independent potential control were used to show that selectively deposited TiO2 coatings can suppress the rate of back reactions on neighboring active sites by an order of magnitude compared with uncoated control samples.

Oxygen vacancy enriched and Cu single-atom contained covalent organic frameworks: A competitive photocatalyst to promote hydrogen evolution under visible light

Oxygen vacancy enriched and Cu single-atom contained covalent organic frameworks: A competitive photocatalyst to promote hydrogen evolution under visible light

Facet-Dependent Photocatalytic Deposition of Metal Nanoparticles Onto Rutile TiO2

Deposition of noble metal nanoparticles onto semiconductor such as TiO2 is important for improving photocatalytic activities with metallic co-catalysts and for achieving plasmon-induced charge separation. In that context, facet-selective deposition of metal nanoparticles is attracting attention. There are many reports on the facet-selective deposition, and the selectivity has been explained in terms of different work functions depending on facets.1,2 However, it is likely that factors other than work function also contribute to the selectivity. Therefore, in this work, we focus also on the number of electrons involved in the reactions and the surface and interfacial energies of the semiconductor and metal, so as to understand the mechanisms of the selective deposition and to control the deposition sites and morphologies of the metal nanoparticles. Here, we employed rutile TiO2 particles with exposed crystal planes as a semiconductor material and deposited Au, Pt, and Ag nanoparticles onto the TiO2 particles by photocatalytic means.Rutile TiO2 particles with exposed crystal planes were synthesized by a flux method. Anatase TiO2 as a precursor was heated at 1000 °C in a NaCl molten salt in air. The TiO2 particles thus obtained (50 mg) was added to 50 vol% aqueous ethanol (5 mL). The solution was purged with nitrogen and a metal precursor, HAuCl4, H2PtCl6, or AgNO3, was added to the solution, followed by irradiating with a UV LED lamp (365 nm) for 10 min, for deposition of Au, Pt, or Ag, respectively, onto the TiO2 particles.From XRD measurements and SEM observation, it was revealed that the obtained TiO2 particles have rutile structure and (110) and (111) planes. The average exposed area ratio between (110) and (111) planes was estimated to be around 7:3. After photocatalytic deposition of Au, we found 87% of the Au nanoparticles were deposited on (110) planes. Even higher selectivity was observed for Pt nanoparticles; 94% of them were deposited on (110) planes. In contrast, interestingly, 75% of Ag nanoparticles were found at (111) planes. Other Ag nanoparticles were found on the edges in between (110) planes. Namely, facet selectivity was different for Au, Pt, and Ag, and the observed difference was difficult to explain solely in terms of work function.We therefore focused on difference in the number of electrons required for the metal deposition reactions. In the case of Au and Pt, these metals are deposited by multi-electron reduction reactions; [AuCl4]- and [PtCl6]2- require 3 and 4 electrons, respectively, to be deposited as metal. It is known that the conduction band minimum of the (110) plane is lower (i.e., more positive in potential) than that of the (111) plane. Therefore, photoexcited electrons should tend to accumulate at (110) planes, and multi-electron reductive deposition of Au and Pt should be promoted there. In contrast, Ag nanoparticles are deposited through one-electron reduction of Ag+, which should not require accumulation of excited electrons, and the deposition occurs even at (111) planes. Because the (111) plane has higher surface energy than the (110) plane, the former could be readily stabilized by coating with Ag, which has much lower surface energy than the rutile TiO2(111) plane. When such an anisotropic growth of metal into nanoplates occurs on a semiconductor, the interfacial energy between them should be low enough. It is expected that a metal crystal lattice is easily distorted to match that of a semiconductor, if the Young's modulus for the metal is low. The Young's modulus of Ag is actually lower than those of Au and Pt,3 indicating that Ag is advantageous to cover the TiO2 surface, even if there is some lattice mismatch between them, resulting in low interfacial energy.In summary, it was shown that facet-selective deposition and morphology control of metal nanoparticles are possible to some extent for rutile TiO2. Also, it was shown that, not only work function, but also the number of electrons involved in the deposition reactions and the surface and interfacial energies for the metal and semiconductor are also important in the facet-selective deposition. These findings would allow us to improve activity of metal co-catalysts and to control plasmon resonance properties of metal nanoparticles.[1] T. Takata, et al., Nature, 581, 411 (2020).[2] R. Li, et al., Nat. Commun., 4, 1432 (2013).[3] C. J. Price and S. P. Hepplestone, J. Mater. Chem. C, 11, 14278 (2023). Figure 1

Area Selective Atomic Layer Deposition for Spatial Control of Reaction Selectivity on Modelphotocatalysts

Photocatalytic water splitting is one promising route to reducing the cost of H2 production to industrially relevant levels. However, these systems are currently limited in their solar-to-hydrogen efficiency requiring further development in designing highly active and selective reaction sites. Reverse reactions, such as hydrogen oxidation or oxygen reduction, can greatly reduce overall system efficiency and are exacerbated by the close proximity of neighboring particles, which creates locally high concentrations of reactants. Metal oxide coatings have previously been used to selectively block undesired reactants from reaching the active sites, but can be limited in their ability to allow two different desired half reactions to occur as required for photocatalysts. In this work, we target selectively-deposited ALD of oxide films (e.g., TiO2 and SiO2) onto metallic co-catalysts for enhancing reaction selectivity while maintaining a high overall activity. Pt and Au were used an exemplary reduction and oxidation co-catalysts sites, where Au was deactivated towards ALD growth through self-assembled thiol monolayers while TiOx coated Pt suppressed Fe(II) redox reactions while maintaining the hydrogen evolution reaction (HER). The efficacy of the selective ALD growth was assessed through ellipsometry and X-ray photoelectron spectroscopy (XPS), while reaction selectivity was assessed through cyclic voltammetry. A planar photocatalyst model of patterned interdigitated arrays of Au and Pt was developed to further assess the selective ALD on the micron scale. Patterned electrodes were evaluated through cross-sectional scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS) and XPS, while reaction selectivity towards the HER over Fe(II) reduction was estimated using scanning electrochemical microscopy (SECM). Finally, interdigitated electrodes were used to simulate the effect of neighboring particle photocatalysts, where selectively deposited TiOx showed a significant reduction in reverse reactions over the uncoated samples.