Oxidatively stable nanoporous silicon photocathodes with enhanced onset voltage for photoelectrochemical proton reduction

Optical properties of black silicon structures ALD-coated with Al2O3

Atomic layer deposited (ALD) Al₂O₃coatings were applied on black silicon (b-Si) structures. The coated nanostructures were investigated regarding their reflective and transmissive behaviour. For a systematic study of the influence of the Al₂O₃coating, ALD coatings with a varying layer thickness were deposited on three b-Si structures with different morphologies. With a scanning electron microscope the morphological evolution of the coating process on the structures was examined. The optical characteristics of the different structures were investigated by spectral transmission and reflection measurements. The usability of the structures for highly efficient absorbers and antireflection (AR) functionalities in the different spectral regions is discussed.

Steering the Pathway of Plasmon-Enhanced Photoelectrochemical CO2 Reduction by Bridging Si and Au Nanoparticles through a TiO2 Interlayer

Photoelectrochemical (PEC) conversion of CO₂ in an aqueous medium into high-energy fuels is a creative strategy for storing solar energy and closing the anthropogenic carbon cycle. However, the rational design of catalytic architectures to selectively and efficiently produce a target product such as CO has remained a grand challenge. Herein, an efficient and selective Si photocathode for CO production is reported by utilizing a TiO₂ interlayer to bridge the Au nanoparticles and n⁺ p-Si. The TiO₂ interlayer can not only effectively protect and passivate Si surface, but can also exhibit outstanding synergies with Au nanoparticles to greatly promote CO₂ reduction kinetics for CO production through stabilizing the key reaction intermediates. Specifically, the TiO₂ layer and Au nanoparticles work concertedly to enhance the separation of localized surface plasmon resonance generated hot carriers, contributing to the improved activity and selectivity for CO production by utilizing the hot electrons generated in Au nanoparticles during PEC CO₂ reduction. The optimized Au/TiO₂ /n⁺ p-Si photocathode exhibits a Faradaic efficiency of 86% and a partial current density of -5.52 mA cm^-2 at -0.8 V_RHE for CO production, which represent state-of-the-art performance in this field. Such a plasmon-enhanced strategy may pave the way for the development of high-performance PEC photocathodes for energy-efficient CO₂ utilization.

Improved hydrogen evolution with SnS2 quantum dot-incorporated black Si photocathode

Black silicon (bSi), possessing appealing light-trapping properties and large specific surface area, ranks high among many other photocathode materials. However, the insufficient dynamics towards HER seriously bother black Si. Herein, a novel photoelectrode with ultrasmall size tin sulfide quantum dot (SnS₂ QD) incorporated black silicon was employed. Nanosized SnS₂ possesses numerous active sites for electrochemical reactions. Impressively, benefiting from SnS₂ QDs, the downward band bending of the Si Fermi level at the interface of electrolyte becomes higher, which remarkably suppresses the recombination of photo-generated carriers, thereby facilitating the participation of photo-generated electrons in PEC-HER. As a result, the thus-designed SnS₂/bSi reveals an exceptional PEC-HER activity with a positive onset potential of 0.235 V vs. reversible hydrogen electrode (RHE), a high photocurrent of 1.23 mA cm^-2 at 0 V vs. RHE, and long-term stability. Besides, the saturated photocurrent of ∼41 mA cm^-2 is achieved at about -0.51 V vs. RHE.

Solution-processed silicon quantum dot photocathode for hydrogen evolution

The photoelectrochemical response of a photocathode made from a colloidal solution of boron (B) and phosphorus (P) codoped silicon (Si) quantum dots (QDs) 2-11 nm in diameters is studied. Since codoped Si QDs are dispersible in alcohol and water due to the hydrophilic surface, a photoelectrode with a smooth surface is produced by drop-coating the QD solution on an indium tin oxide substrate. The codoping provides high oxidation resistance to Si QDs and makes the electrode operate as a photocathode. The photoelectrochemical response of a Si QD photoelectrode depends strongly on the size of QDs; there is a transition from anodic to cathodic photocurrent around 4 nm in diameter. Below the size, anodic photocurrent due to self-oxidation of Si QDs is observed, while above the size, cathodic photocurrent due to electron transfer across the interface is observed. The cathodic photocurrent increases with increasing the size, and in some samples, it is observed for more than 3000 s under intermittent light irradiation.

Copper-assisted catalyzed etching for nanotextured black silicon with enhanced photoelectric-conversion properties

Black silicon contains high-aspect-ratio micro/nanostructures with greatly suppressed front-surface reflection, thus possessing superior property in photoelectric devices. In this report, by a two-step copper-assisted chemical etching method, we have fabricated pyramid n⁺p-black silicon with optimized morphology and anti-reflectance capability, through systematically tuning the concentration of both copper ions and reducing agents, as well as the etching time. The improved optical absorption and superior charge transfer kinetics validate n⁺p-black silicon as a highly active photocathode in photoelectrochemical cells. The onset potential of 0.21 V vs. RHE and the saturation photocurrent density of 32.56 mA/cm² are achieved in the optimal n⁺p-black silicon. In addition, the nanoporous structure with lower reflectance is also achieved in planar p-silicon via the same etching method. Moreover, the photodetectors based on planar p-black silicon show significantly enhanced photoresponsivity over a broad spectral range. This study offers a low-cost and scalable strategy to improve the photoelectric-conversion efficiency in silicon-based devices.

2-Aminobenzenethiol-Functionalized Silver-Decorated Nanoporous Silicon Photoelectrodes for Selective CO2 Reduction

A molecularly thin layer of 2-aminobenzenethiol (2-ABT) was adsorbed onto nanoporous p-type silicon (b-Si) photocathodes decorated with Ag nanoparticles (Ag NPs). The addition of 2-ABT alters the balance of the CO₂ reduction and hydrogen evolution reactions, resulting in more selective and efficient reduction of CO₂ to CO. The 2-ABT adsorbate layer was characterized by Fourier transform infrared (FTIR) spectroscopy and modeled by density functional theory calculations. Ex situ X-ray photoelectron spectroscopy (XPS) of the 2-ABT modified electrodes suggests that surface Ag atoms are in the +1 oxidation state and coordinated to 2-ABT via Ag-S bonds. Under visible light illumination, the onset potential for CO₂ reduction was -50 mV vs. RHE, an anodic shift of about 150 mV relative to a sample without 2-ABT. The adsorption of 2-ABT lowers the overpotentials for both CO₂ reduction and hydrogen evolution. A comparison of electrodes functionalized with different aromatic thiols and amines suggests that the primary role of the thiol group in 2-ABT is to anchor the NH₂ group near the Ag surface, where it serves to bind CO₂ and also to assist in proton transfer.

Superaerophobic hydrogels for enhanced electrochemical and photoelectrochemical hydrogen production

The efficient removal of gas bubbles in (photo)electrochemical gas evolution reactions is an important but underexplored issue. Conventionally, researchers have attempted to impart bubble-repellent properties (so-called superaerophobicity) to electrodes by controlling their microstructures. However, conventional approaches have limitations, as they are material specific, difficult to scale up, possibly detrimental to the electrodes' catalytic activity and stability, and incompatible with photoelectrochemical applications. To address these issues, we report a simple strategy for the realization of superaerophobic (photo)electrodes via the deposition of hydrogels on a desired electrode surface. For a proof-of-concept demonstration, we deposited a transparent hydrogel assembled from M13 virus onto (photo)electrodes for a hydrogen evolution reaction. The hydrogel overlayer facilitated the elimination of hydrogen bubbles and substantially improved the (photo)electrodes' performances by maintaining high catalytic activity and minimizing the concentration overpotential. This study can contribute to the practical application of various types of (photo)electrochemical gas evolution reactions.

Direct In Situ Growth of Centimeter-Scale Multi-Heterojunction MoS2/WS2/WSe2 Thin-Film Catalyst for Photo-Electrochemical Hydrogen Evolution

To date, the in situ fabrication of the large-scale van der Waals multi-heterojunction transition metal dichalcogenides (multi-TMDs) is significantly challenging using conventional deposition methods. In this study, vertically stacked centimeter-scale multi-TMD (MoS2/WS2/WSe2 and MoS2/WSe2) thin films are successfully fabricated via sequential pulsed laser deposition (PLD), which is an in situ growth process. The fabricated MoS2/WS2/WSe2 thin film on p-type silicon (p-Si) substrate is designed to form multistaggered gaps (type-II band structure) with p-Si, and this film exhibits excellent spatial and thickness uniformity, which is verified by Raman spectroscopy. Among various application fields, MoS2/WS2/WSe2 is applied to the thin-film catalyst of a p-Si photocathode, to effectively transfer the photogenerated electrons from p-Si to the electrolyte in the photo-electrochemical (PEC) hydrogen evolution. From a comparison between the PEC performances of the homostructure TMDs (homo-TMDs)/p-Si and multi-TMDs/p-Si, it is demonstrated that the multistaggered gap of multi-TMDs/p-Si improves the PEC performance significantly more than the homo-TMDs/p-Si and bare p-Si by effective charge transfer. The new in situ growth process for the fabrication of multi-TMD thin films offers a novel and innovative method for the application of multi-TMD thin films to various fields.

Graphdiyne Nanowall for Enhanced Photoelectrochemical Performance of Si Heterojunction Photoanode

Graphdiyne (GDY), a new member of 2D carbon material family, was introduced into a Si heterojunction (SiHJ)-based photoelectrochemical water splitting cell. With assistance of magnetron-sputtered NiO_x, the plateau photocurrent density of SiHJ/GDY/NiO _x-10 nm with optimized NiO _x film thickness was twice higher than that of SiHJ/NiO _x-10 nm, demonstrating the catalytic function of GDY itself as well as the synergistic effect between GDY and NiO _x. The results verified that GDY is a promising photoelectrode material candidate to realize highly efficient PEC performance, and pave a novel pathway to further improve Si-based PEC system.

Wafer-Scale Ultrathin, Single-Crystal Si and GaAs Photocathodes for Photoelectrochemical Hydrogen Production

Crystalline Si and III-V compound semiconductors with appropriate band edge positions for the reduction of water have been widely utilized in photoelectrochemical (PEC) cells for the hydrogen evolution reaction (HER). However, the high cost of manufacturing those PEC cell photoabsorbers makes it difficult to achieve cost-effective hydrogen production. To overcome this issue, a new approach to fabricate a photoabsorber with low cost yet high performance for the HER is highly necessary. Here, we present a controlled fracture method, the so-called spalling process, to fabricate a cost-effective thin semiconductor applicable to the PEC HER. Using this method, a wafer-scale thin Si, whose thickness can be controlled from a few micrometers to sub-50 μm, was fabricated from a thick Si mother substrate without material loss. Pt nanoparticle-decorated 16 μm thick spalled Si with an np⁺ rear junction exhibited an HER onset potential of 332 mV (vs reversible hydrogen electrode (RHE)) and a photocurrent density of 20.1 mA cm^-2 at 0 V (vs RHE), which are the best performances among previously reported planar-type thin Si-based photocathodes. Finally, we demonstrated that 20 μm thick GaAs could also be successfully fabricated by the spalling process, while exhibiting a PEC HER performance comparable to 350 μm thick bulk GaAs.

Dynamic Photoelectrochemical Device with Open-Circuit Potential Insensitive to Thermodynamic Voltage Loss

The open-circuit potential ( V_oc) represents the maximum thermodynamic potential in a device, and achieving a high V_oc is crucial for self-biased photoelectrochemical (PEC) devices that use only solar energy to produce chemical energy. In general, V_oc is limited by the photovoltage ( V_ph), which is a potential difference generated by light-induced thermodynamic processes at semiconductor photoelectrodes, such as the generation and recombination of charge carriers. Therefore, low light intensity and nanostructured semiconductor materials degrade V_ph (and V_oc) by inefficient carrier generation and by enhancing recombination loss, respectively. Here, we report that V_oc in dynamic PEC devices employing a porous NiO _x/Si photocathode is insensitive to thermodynamic losses, which was clarified by varying the carrier generation and recombination rates. The V_oc values were observed to be unchanged even under a low light intensity of 0.1 sun, as well as for different morphologies such as nanostructured and polycrystalline Si. These findings shed light on the potential merit of dynamically operated PEC systems.

Photoelectrochemical Characterisation on Surface-Inverted Black Silicon Photocathodes by Using Platinum/Palladium Co-catalysts for Solar-to-Hydrogen Conversion

Black silicon (bSi) has recently captured research attention in photoelectrochemical (PEC) solar-to-hydrogen (STH) conversion devices. Because nanostructuring of silicon retains the photovoltaic attributes of the material, it also provides a range of excellent physicochemical properties, such as a vast active-site-rich electrochemical interface, owing to a high aspect ratio, and important light-scattering attributes, which significantly improve photoconversion. One method to gain control over p-type bSi interface energetics is surface inversion of the p-type interface by phosphorus doping to introduce a shallow n⁺ -emitter layer, which provides a thin p-n junction at the interface of the nanostructures. Although this concept has been suggested in the literature, it has not been demonstrated experimentally for a platinum/palladium co-catalysed bSi photocathode device for STH conversion. Herein, preliminary investigations and proof-of-concept studies are reported for the fabrication and PEC characterisation of surface-inverted p-type bSi photocathodes prepared by wet chemical etching. The PEC tests on p-bSi|n⁺ photocathodes show that, for both metal nanoparticles (Pt and Pd), the catalytic activity for proton conversion is increased; this is evident from an anodic shift in the onset potentials shifts to 0.24 and 0.29 V and an increase in photocurrent by 9 and 13.8 mA cm^-2 , respectively, at 0 V versus a reversible hydrogen electrode, as a result of introducing the emitter layer.

Dynamic Photoelectrochemical Device Using an Electrolyte-Permeable NiO x/SiO2/Si Photocathode with an Open-Circuit Potential of 0.75 V

As a thermodynamic driving force obtained from sunlight, the open-circuit potential (OCP) in photoelectrochemical cells is typically limited by the photovoltage ( V_ph). In this work, we establish that the OCP can exceed the value of V_ph when an electrolyte-permeable NiO _x thin film is employed as an electrocatalyst in a Si photocathode. The built-in potential developed at the NiO _x/Si junction is adjusted in situ according to the progress of the NiO _x hydration for the hydrogen evolution reaction (HER). As a result of decoupling of the OCP from V_ph, a high OCP value of 0.75 V (vs reversible hydrogen electrode) is obtained after 1 h operation of HER in an alkaline electrolyte (pH = 14), thus outperforming the highest value (0.64 V) reported to date with conventional Si photoelectrodes. This finding might offer insight into novel photocathode designs such as those based on tandem water-splitting systems.

Controlled growth of vertically aligned ultrathin In2S3 nanosheet arrays for photoelectrochemical water splitting

This paper reports a facile solvothermal method for the in situ growth of vertically aligned In₂S₃ nanosheet arrays (NSAs) on fluorine-doped tin oxide substrates. The as-synthesized two-dimensional graphene-like In₂S₃ nanosheets show an ultrathin thickness down to 3.7 nm consisting of the duodenary interplanar spacing of the (222) plane and a tunable bandgap varying from 2.32 to 2.58 eV. The film thickness and nanosheet density of the In₂S₃ NSAs can be adjusted by varying the reaction time and precursor concentration. The In₂S₃ NSAs with a higher film thickness exhibit relatively higher photocurrent due to their stronger light absorption as well as larger surface area for sufficient charge separation and redox reaction. The photoelectrochemical performance of the In₂S₃ photoanodes can be greatly enhanced by constructing an effective heterojunction with ZnO to promote the photocarrier separation. The In₂S₃/ZnO NSAs have demonstrated an optimal photocurrent density of 349.1 μA cm^-2 at 1.2 V vs. RHE and a maximum incident photon to current efficiency of 10.26% at 380 nm, which are 13.5 and 38 times higher than those of the pristine In₂S₃ counterparts, respectively.

Semiconductor-Based Photoelectrochemical Conversion of Carbon Dioxide: Stepping Towards Artificial Photosynthesis

The photoelectrochemical (PEC) carbon dioxide reduction process stands out as a promising avenue for the conversion of solar energy into chemical feedstocks, among various methods available for carbon dioxide mitigation. Semiconductors derived from cheap and abundant elements are interesting candidates for catalysis. Whether employed as intrinsic semiconductors or hybridized with metallic cocatalysts, biocatalysts, and metal molecular complexes, semiconductor photocathodes exhibit good performance and low overpotential during carbon dioxide reduction. Apart from focusing on carbon dioxide reduction materials and chemistry, PEC cells towards standalone devices that use photohybrid electrodes or solar cells have also been a hot topic in recent research. An overview of the state-of-the-art progress in PEC carbon dioxide reduction is presented and a deep understanding of the catalysts of carbon dioxide reduction is also given.

Silicon Photoelectrode Thermodynamics and Hydrogen Evolution Kinetics Measured by Intensity-Modulated High-Frequency Resistivity Impedance Spectroscopy

We present an impedance technique based on light intensity-modulated high-frequency resistivity (IMHFR) that provides a new way to elucidate both the thermodynamics and kinetics in complex semiconductor photoelectrodes. We apply IMHFR to probe electrode interfacial energetics on oxide-modified semiconductor surfaces frequently used to improve the stability and efficiency of photoelectrochemical water splitting systems. Combined with current density-voltage measurements, the technique quantifies the overpotential for proton reduction relative to its thermodynamic potential in Si photocathodes coated with three oxides (SiO_x, TiO₂, and Al₂O₃) and a Pt catalyst. In pH 7 electrolyte, the flatband potentials of TiO₂- and Al₂O₃-coated Si electrodes are negative relative to samples with native SiO_x, indicating that SiO_x is a better protective layer against oxidative electrochemical corrosion than ALD-deposited crystalline TiO₂ or Al₂O₃. Adding a Pt catalyst to SiO_x/Si minimizes proton reduction overpotential losses but at the expense of a reduction in available energy characterized by a more negative flatband potential relative to catalyst-free SiO_x/Si.

Electrochemical Growth of Copper Hydroxy Double Salt Films and Their Conversion to Nanostructured p-Type CuO Photocathodes

New electrochemical synthesis methods were developed to produce copper hydroxy double salt(Cu-HDS) films with four different intercalated anions (NO₃^-, SO₄^2-, Cl^-, and dodecyl sulfate (DS)) as pure crystalline films as deposited (Cu₂NO₃(OH)₃, Cu₄SO₄(OH)₆, Cu₂Cl(OH)₃, and Cu₂DS(OH)₃). These methods are based on p-benzoquinone reduction, which increases the local pH at the working electrode and triggers the precipitation of Cu²⁺ and appropriate anions as Cu-HDS films on the working electrode. The resulting Cu-HDS films could be converted to crystalline Cu(OH)₂ and CuO films by immersing them in basic solutions. Because Cu-HDS films were composed of 2D crystals as a result of the atomic-level layered structure of HDS, the CuO films prepared from Cu-HDS films have unique low-dimensional nanostructures, creating high surface areas that cannot be obtained by direct deposition of CuO, which has a 3D atomic-level crystal structure. The resulting nanostructures allowed the CuO films to facilitate electron-hole separation and demonstrate great promise for photocurrent generation when investigated as a photocathode for a water-splitting photoelectrochemical cell. Electrochemical synthesis of Cu-HDS films and their facile conversion to CuO films will provide new routes to tune the morphologies and properties of the CuO electrodes that may not be possible by other synthesis means.

Enhanced PEC performance of nanoporous Si photoelectrodes by covering HfO2 and TiO2 passivation layers

Nanostructured Si as the high efficiency photoelectrode material is hard to keep stable in aqueous for water splitting. Capping a passivation layer on the surface of Si is an effective way of protecting from oxidation. However, it is still not clear in the different mechanisms and effects between insulating oxide materials and oxide semiconductor materials as passivation layers. Here, we compare the passivation effects, the photoelectrochemical (PEC) properties, and the corresponding mechanisms between the HfO2/nanoporous-Si and the TiO2/nanoporous-Si by I-V curves, Motte-schottky (MS) curves, and electrochemical impedance spectroscopy (EIS). Although the saturated photocurrent densities of the TiO2/nanoporous Si are lower than that of the HfO2/nanoporous Si, the former is more stable than the later.

Tuning the Photoelectrocatalytic Hydrogen Evolution of Pt-Decorated Silicon Photocathodes by the Temperature and Time of Electroless Pt Deposition

The electroless deposition of Pt nanoparticles (NPs) on hydrogen-terminated silicon (H-Si) surfaces is studied as a function of the temperature and the immersion time. It is demonstrated that isolated Pt structures can be produced at all investigated temperatures (between 22 and 75 °C) for short deposition times, typically within 1-10 min if the temperature is 45 °C or less than 5 min at 75 °C. For longer times, dendritic metal structures start to grow, ultimately leading to highly rough interconnected Pt networks. Upon increasing the temperature from 22 to 75 °C and for an immersion time of 5 min, the average size of the observed Pt NPs monotonously increases from 120 to 250 nm, and their number density calculated using scanning electron microscopy decreases from (4.5 ± 1.0) × 10⁸ to (2.0 ± 0.5) × 10⁸ Pt NPs cm^-2. The impact of both the morphology and the distribution of the Pt NPs on the photoelectrocatalytic activity of the resulting metallized photocathodes is then analyzed. Pt deposited at 45 °C for 5 min yields photocathodes with the best electrocatalytic activity for the hydrogen evolution reaction. Under illumination at 33 mW cm^-2, this optimized photoelectrode shows a fill factor of 45%, an efficiency (η) of 9.7%, and a short-circuit current density (|J_sc|) at 0 V versus a reversible hydrogen electrode of 15.5 mA cm^-2.

Silicon Nanowire Photocathodes for Photoelectrochemical Hydrogen Production

The performance of silicon for water oxidation and hydrogen production can be improved by exploiting the antireflective properties of nanostructured silicon substrates. In this work, silicon nanowires were fabricated by metal-assisted electroless etching of silicon. An enhanced photocurrent density of -17 mA/cm² was observed for the silicon nanowires coated with an iron sulphur carbonyl catalyst when compared to bare silicon nanowires (-5 mA/cm²). A substantial amount of 315 µmol/h hydrogen gas was produced at low bias potentials for the silicon nanowires coated with an iron sulphur carbonyl catalyst.

Proton Reduction Using a Hydrogenase-Modified Nanoporous Black Silicon Photoelectrode

Metalloenzymes featuring earth-abundant metal-based cores exhibit rates for catalytic processes such as hydrogen evolution comparable to those of noble metals. Realizing these superb catalytic properties in artificial systems is challenging owing to the difficulty of effectively interfacing metalloenzymes with an electrode surface in a manner that supports efficient charge-transfer. Here, we demonstrate that a nanoporous "black" silicon (b-Si) photocathode provides a unique interface for binding an adsorbed [FeFe]-hydrogenase enzyme ([FeFe]-H2ase). The resulting [FeFe]-H2ase/b-Si photoelectrode displays a 280 mV more positive onset potential for hydrogen generation than bare b-Si without hydrogenase, similar to that observed for a b-Si/Pt photoelectrode at the same light intensity. Additionally, we show that this H2ase/b-Si electrode exhibits a turnover frequency of ≥1300 s(-1) and a turnover number above 10(7) and sustains current densities of at least 1 mA/cm(2) based on the actual surface area of the electrode (not the smaller projected geometric area), orders of magnitude greater than that observed for previous enzyme-catalyzed electrodes. While the long-term stability of hydrogenase on the b-Si surface remains too low for practical applications, this work extends the proof-of-concept that biologically derived metalloenzymes can be interfaced with inorganic substrates to support technologically relevant current densities.

Carbon quantum dots decorated Cu2S nanowire arrays for enhanced photoelectrochemical performance

The photoelectrochemical (PEC) performance of Cu2S nanowire arrays (NWAs) has been demonstrated to be greatly enhanced by dipping-assembly of carbon quantum dots (CQDs) on the surfaces of Cu2S NWAs. Experimental results show that the pristine Cu2S NWAs with higher aspect ratios exhibit better PEC performance due to the longer length scale for light absorption and the shorter length scale for minority carrier diffusion. Importantly, the CQDs decorated Cu2S NWAs exhibit remarkably enhanced photocurrent density, giving a photocurrent density of 1.05 mA cm(-2) at 0 V vs. NHE and an optimal photocathode efficiency of 0.148% under illumination of AM 1.5G (100 mW cm(-2)), which is 4 times higher than that of the pristine Cu2S NWAs. This can be attributed to the improved electron transfer and the energy-down-shift effect of CQDs. We believe that this inexpensive Cu2S/CQD photocathode with increased photocurrent density opens up new opportunities in PEC water splitting.

The diameter-dependent photoelectrochemical performance of silicon nanowires

We demonstrate the first systematic study of the diameter-dependent photoelectrochemical performance of single silicon nanowires within a broad size range from 200 to 2000 nm.

High performance nanoporous silicon photoelectrodes co-catalyzed with an earth abundant [Mo3S13]2− nanocluster via drop coating

Earth abundant [Mo₃S₁₃]²⁻ nanoclusters efficiently enhance a nanoporous silicon photoelectrode for hydrogen generation.