Solar-driven Water Research Articles

Improved solar-driven water purification using an eco-friendly and cost-effective aerogel-based interfacial evaporator with exceptional photocatalytic capabilities

As a promising solution to address the global challenge of freshwater scarcity, solar-powered interfacial steam generation has undergone notable advancements. This study introduces a novel solar-driven interfacial evaporation membrane (ZnIn2S4@SiO2/ACSA, ZSAS) comprising a ZnIn2S4@SiO2 composite and a black sodium alginate aerogel infused with activated carbon. The ZSAS membrane demonstrates exceptional light absorption and thermal insulation, leading to elevated surface temperatures and reduced heat dissipation into the bulk water. Furthermore, the incorporation of AC reinforces the mechanical properties of the ZSAS membrane and enhances the water purification performance. These collective features result in an impressive evaporation rate of 1.485 kg m−2 h−1 and a high photothermal conversion efficiency of 91.2% under 1 sun irradiation for the optimal ZSAS membrane. Moreover, the optimal ZSAS membrane can effectively remove salts, heavy metal ions, and organic pollutants, benefitting from its superior evaporation separation effect and the photocatalytic properties of the ZnIn2S4@SiO2 composite.

Flexible hierarchical polypyrrole-coated Cu-BTC MOFs photothermal textile for efficiently solar water evaporation and wastewater purification

Solar-driven interfacial water evaporation (SDIWE) endures a significant potential for producing clean water from seawater and wastewater because it requires no additional energy source. Photothermal materials with efficient solar absorption and pollutant removal capabilities are critical for SDIWE. However, an efficient and facile strategy to prepare a high-performance and flexible photothermal material and simultaneously prevent the salt accumulation for efficient and long-term steady evaporation to produce potable water from seawater and wastewater is still a challenge. Herein, based on the MS and ALD processes, two novel flexible photothermal materials are synthesized using the flexible polyester fabric substrate, hierarchical metal–organic framework Cu-BTC MOFs, and polypyrrole (PPy) as a light-absorption layer. In particular, under the synergistic effect of the hierarchical porous Cu-BTC MOFs and PPy with excellent solar absorption, the flexible photothermal material possesses excellent light absorption (92.58 % ∼ 93.98 %), super hydrophilicity, low thermal conductivity, high evaporation rate (1.53 ∼ 1.56 kg m-2h−1 for 15 days), outstanding salt resistance (1.42 kg m-2h−1 at a salinity of 15 wt%), and excellent metal ions and organic pollutants removal capacity after solar evaporation. These multifunctional properties ensure its great application prospect for future freshwater production while also providing a new reference for other applications.

MXene/Cellulose Composite Cloth for Integrated Functions (if-Cloth) in Personal Heating and Steam Generation

Given the abundant solar light available on our planet, it is promising to develop an advanced fabric capable of simultaneously providing personal thermal management and facilitating clean water production in an energy-efficient manner. In this study, we present the fabrication of a photothermally active, biodegradable composite cloth composed of titanium carbide MXene and cellulose, achieved through an electrospinning method. This composite cloth exhibits favorable attributes, including chemical stability, mechanical performance, structural flexibility, and wettability. Notably, our 0.1-mm-thick composite cloth (RC/MXene IV) raises the temperature of simulated skin by 5.6 °C when compared to a commercially available cotton cloth, which is five times thicker under identical ambient conditions. Remarkably, the composite cloth (RC/MXene V) demonstrates heightened solar light capture efficiency (87.7%) when in a wet state instead of a dry state. Consequently, this cloth functions exceptionally well as a high-performance steam generator, boasting a superior water evaporation rate of 1.34 kg m−2 h−1 under one-sun irradiation (equivalent to 1000 W m−2). Moreover, it maintains its performance excellence in solar desalination processes. The multifunctionality of these cloths opens doors to a diverse array of outdoor applications, including solar-driven water evaporation and personal heating, thereby enriching the scope of integrated functionalities for textiles.Graphical

Novel Strategies for Efficient Water Electrolysis

A growing global population in parallel with an increased prosperity seen from a global perspective have raised the need for energy and raw material resources exponentially. These increased needs have led to a number of negative consequences such as pollution, raw material shortages, increasing carbon dioxide levels in the atmosphere, and not least a threatening global warming. Renewable energy will be essential to break the dependence of fossil fuels, but due to the intermittency of renewables a storable non-fossil alternative is needed. Hydrogen represents one of very few sustainable options to store renewable energy on large scale and for seasonal variations. Here, we present novel strategies on water electrolysis driven by photovoltaics, with a focus on the development of state-of the art electrocatalysts based on earth-abundant transition metals, doped with sulphur and phosphor [1]. We show that by tuning parameters such as adsorption energy, morphology and conductance of the electrocatalysts we can achieve solar-to hydrogen efficiency approaching 20 % [2]. We discuss on strategies, mechanisms and challenges in the field of PV-driven electrolysis.[1] Ekspong, J; Larsen, C; Stenberg, J;, Kwong, WL; Wang, J; Zhang, J; Johansson, EM; Messinger, J; Edman, L; Wagberg T, Solar-Driven Water Splitting at 13.8% Solar-to-Hydrogen Efficiency by an Earth-Abundant Electrolyzer, ACS Sustainable Chemistry & Engineering, sc-2021-03565f (acssuschemeng.1c03565). (2021)[2] H Zhang, A Aierke, Y Zhou, Z Ni, L Feng, A Chen, T Wågberg, G Hu, A high‐performance transition‐metal phosphide electrocatalyst for converting solar energy into hydrogen at 19.6% STH efficiency, Carbon Energy, 5 (1), e217 (2022)

Characterization of the Photothermal Response in Nanocomposite Silica Aerogel Materials with Thin Metal Films

The photothermal effect, whereby light energy is converted into thermal energy when absorbed in a material, is a phenomenon that has many potential applications including solar-driven water heating and purification, and radiative heat transfer. Recently, porous materials have been tailored to exhibit the photothermal effect to be used for interfacial water evaporation and sterilization. In this work we provide the characterization of the solar-driven photothermal effect on nanocomposite aerogel materials. Aerogels exhibit a unique combination of properties that can enhance their utility as a photothermal material. Due to their inherently low density and thermal conductivity, and their exceptional insulative properties, photothermal heat generated within an aerogel can remain trapped. This work presents the photothermal effect in nanocomposite aerogels fabricated by sputtering metal and metal oxide films onto and into aerogels materials. By sputtering metal and metal oxides in a high vacuum environment and directing it towards an aerogel substrate using a magnetron, we were able to deposit thin films onto the surface of an aerogel. The composite aerogels are characterized using scanning electron microscopy (SEM) to assess the depth of the sputtered material into the aerogel pores. The reflectance and transmittance of the aerogel composites are measured using UV-Vis spectroscopy. The photothermal effect in aerogel composites is measured using thermal imaging. Our results show that the photothermal response of the composite aerogels can be tuned by varying the thickness and composition of the deposited films. Overall, our study demonstrates the potential of using magnetron sputtering to create composite aerogels with tailored photothermal properties. This opens new opportunities for a wide range of applications such as water and air heating and purification, water desalination, and solar energy harvesting devices.

Solar Water Splitting Device Integrated Carbon-Based Electrodes and Carbon-Based Perovskite Solar Cells

Producing hydrogen from integrated devices by solar-driven water splitting (SWS) is one of the most attractive methods for renewable energy conversion. However, their widespread use is hindered by their cost and poor performance. In this work, we developed an integrated device consisting of three series-connected carbon-based multi-porous-layered-electrode perovskite solar cells (MPLE-PSCs) 1-5 and carbon-based catalyst-decorated electrode couples (Figure 1a). Porous carbon electrodes with a graphite and carbon black mixture are used for the back contacts of solar cells, and pencil-lead graphite rods (PGRs) are used as electrocatalyst supports for water-splitting cells, which are much cheaper than existing materials. The performance of the PSC was compared between the 2 and 3-series, and the performance of the water-splitting cell with/without catalyst. In addition, each combination was compared.The solar to electricity efficiency (STE, same as power conversion efficiency: PCE) was 13.79% and 13.16% for the 2-series and 3-series, respectively. The electricity to hydrogen efficiency (ETH), calculated as V theoritical/V operating, 6 was 78.34% and 84.83%, for PGR and NiFe/PGR respectively. Furthermore, the matching factor (MF), calculated as (V operating × J operating)/(V max × J max), 6 for the <2-series PSCs>/<PGR> combination and the <3-series PSCs>/<NiFe/PGR> combination were 48.57% and 83.77%, respectively. Solar to hydrogen efficiency (STE), calculated as STE ×ETH × MF, improved from 5.25% to 9.35% for the optimized device (Figure 1b). These results show that low-cost and high-efficiency solar hydrogen can be produced by using Earth-abundant materials and by adjusting the maximum output of the device.(1) A. Mei, et al., Science 345, 295 (2014).(2) R. Tsuji, et al., Electrochemistry 88, 418 (2020).(3) R. Tsuji, et al., Photonics 7, 133 (2020).(4) D. Bogachuk, R. Tsuji, et al., Carbon 178, 10 (2021).(5) E. Kobayashi, R. Tsuji, et al., Cell Rep. Phys. Sci. 2, 100648 (2021).(6) Z. N. Zahran, et al., ACS Appl. Energy Mater. 5, 8241 (2022).Figure 1. Carbon-based solar water splitting. (a) Schematic diagram and (b) J-V curves of MPLE-PSCs and LSV curves of water electrolysis with PGR electrodes. Figure 1

Nanoengineered Bifunctional Porous Ni5P4 Electrocatalyst with Accelerated Bubble Departure and Reduced Overpotential for Solar-Driven Water Splitting

To achieve the global "carbon neutral" goal and low-carbon economy by 2050-2100, hydrogen has been considered as an ideal renewable and sustainable energy carrier.1,2 The electrochemical conversion of solar energy to energy dense hydrogen fuel ensures a promising approach to generate a clean and sustainable source of energy.3,4 The integrated solar powered water electrolyzers for green hydrogen production completely eliminate all sources of carbon emissions arising from the direct power supply, towards achieving a low-carbon economy.5,6 However, large-scale solar water splitting for green hydrogen production still remains a challenge due to expensive electrocatalyst. As a low-cost, earth-abundant catalyst Nickel phosphide shows enormous potential to effectively reduce water and generate hydrogen. We propose a low-cost and facile approach to fabricate nanoengineered hierarchically porous Ni5P4 as an electrocatalyst (p-Ni5P4) providing high surface area and enabling fast gas diffusion. Nickel phosphide (p-Ni5P4@NF) has pores ranging from 50-500 nm to 200-600 μm and enlarges the electrochemically-active surface area by 5 times. The porous structure of p-Ni5P4@NF offers abundant cavities to gas nucleation and fast growth of H2 bubble, and small bubbles (10-50 µm) depart quickly owing to reduced contact line. By enhancing gas transfer and reducing bubble overpotential by 30%, p-Ni5P4@NF achieves excellent electrocatalytic performance with a low HER (145 mV), OER (197 mV) and overall water splitting potential (1.54 V) at 10 mA cm-2. Powered by multijunction PV cell, the full electrolytic cell records a high solar-to-hydrogen efficiency of 14.5 %. Keywords: Water splitting; Electrocatalysis; Green Hydrogen; Nickel Phosphide.

The Effect of Oxygen Vacancies on Oxygen Evolution: The Case of BiVO_4

Bismuth vanadate, BiVO4, is one of the most promising photoanode materials for the challenging oxygen evolution half-reaction in solar-driven water splitting. The material tends to be rich in oxygen vacancies, which strongly affects its photoelectrochemical properties. Experimental evidence suggests that oxygen deficiency is beneficial for the oxygen evolution reaction in the material, but the mechanism behind this enhancement is still controversial. The defects could be involved directly in the reaction if present at the surface, and the occupancy of the defect states could also play an important role. The latter is seldom considered in mechanistic studies, however.Using density functional theory, we show that the surface oxygen vacancy in bismuth vanadate is stablest when fully ionized. We investigate how this affects the oxygen evolution mechanism by mapping out the stablest reaction intermediates and compare the resulting pathway with those on the unionized oxygen-deficient surface as well as the defect-free material. The overpotentials required to drive the reaction in each case are computed to quantify whether or not vacancy formation, and subsequent ionization, improves the thermodynamics of oxygen evolution.

Enhanced solar-driven thermoelectric power generation and water desalination via hydrothermally synthesized degenerately doped copper selenide nanocrystals composited with polydimethylsiloxane

In this study, we developed novel composites of degenerately doped copper selenide and polydimethylsiloxane (DDCS/PDMS) that efficiently harness a wide range of solar light for both electricity generation and water purification. The DDCS nanocrystals possess remarkable optical absorption capabilities across the near-infrared (NIR) solar spectrum, leading to enhanced photothermal effects. Within the DDCS/PDMS composite, this results in remarkable light-to-heat conversion, sustaining a consistent surface temperature of 51.5 °C in contrast to the 39.8 °C exhibited by bare PDMS when subjected to standard 1 sun intensity for 3 min, and leveraging its exceptional photothermal characteristics, the composite demonstrated noteworthy thermoelectric power generation, achieving 95 mV, while pristine PDMS only managed 49 mV under 1 sun conditions. Moreover, the DDCS/PDMS foam demonstrated outstanding solar-to-vapor performance, achieving a rate of 1.71 Kg m−2 h−1 with an efficiency of 91.5 % under equivalent sunlight exposure. Remarkably, the versatile DDCS/PDMS foam effectively demonstrated its capability in seawater desalination, achieving an efficiency exceeding 80 % even under the most challenging conditions. This study uncovers the compelling potential of solar-thermal energy utilization and introduces an innovative approach for solar-driven water purification and power generation. By addressing the challenges of sustainable energy and clean water provision, these findings offer a promising avenue forward.

Improving photocatalytic hydrogen generation of g-C3N4 via efficient charge separation imposed by Bi2O2Se nanosheets

Enabling highly efficient photocatalytic hydrogen production from solar-driven water splitting is of immense potential and environmental significance. However, the crucial issue of the low utilization efficiency of photogenerated charges in most photocatalysts, such as polymeric graphitic carbon nitride, g-C3N4 (CN), hampers the overall photocatalytic activity and hinders practical applications. To surmount this parasitic phenomenon, we develop a heterojunction-based strategy that improves the charge separation efficiency in CN. The heterostructure is constructed between thermally exfoliated CN and liquid phase exfoliated Bi2O2Se (BOS) via a solution-phase, electrostatically driven self-assembly process. The properly aligned band positions between the two components create a built-in electric field, which endows the composite with an enhanced charge separation efficiency. The optimized Pt-deposited heterostructure photocatalyst exhibits a hydrogen production rate of 6481 μmol h−1 g−1, and an apparent quantum efficiency of 11.65% at 420 nm, compared to those of Pt-deposited ECN (4595 μmol h−1 g−1, 6.64 %). We validate the efficient charge separation effect and the prolonged lifetime of photogenerated carriers in the heterostructure using a series of comprehensive characterizations across multiple timescales, thus, elucidating the origin of the observed photocatalytic activity. This demonstration offers valuable insights into improving the utilization efficiency of photogenerated charges for photocatalysis by heterostructure engineering with materials of distinct electronic configurations.

Economic and environmental protection high efficiency solar steam generator: Carbonized starch with porous structure

Solar-driven interfacial water evaporation is an emerging water purification technology. However, the high cost and low evaporation efficiency limit the wide application of solar-driven interfacial water evaporation technology. In this work, we use the dough fermented flour and yeast powder production, and then after fermentation of dough to produce high temperature carbonization of carbon materials, the preparation of the sample surface formed a large number of pits, increased specific surface area and the absorbance of the sample, and increased the solar-thermal conversion efficiency of the sample. It is found that the evaporation rate and evaporation efficiency of the sample made in this work is 1.5 kg m−2h−1 and 94.2 % respectively under one solar irradiation intensity. The maximum surface temperature of the sample can reach 43.3℃ during the experimental test, which has good evaporation performance. It provides a new idea for making economical and environmentally friendly materials in the field of solar-driven water evaporation.

Silicon-based heterojunction photoanodes modified with copper-bipyridine catalyst for enhanced solar-driven water splitting

In photoelectrochemical (PEC) water splitting, accelerating the carrier transfer from the semiconductor to the catalytic functional layer through the construction of nanostructure-heterojunction interface is an effective method to overcome the intrinsically slow kinetics of the photoanode phase interface. In this work, p-type NiO and n-type TiO2 layers were deposited on the surface of n-type Si electrodes, respectively, to construct p-n and n-n heterojunction photoanodes. Moreover, a copper-bipyridine molecular catalyst, namely Cu(dcbpy), was deposited on the heterojunction photoanodes to furtherly provide transfer path for the photogenerated holes in water splitting. Under the illumination of simulated sunlight, the Si/NiO/Cu(dcbpy) photoanode exhibits a high photocurrent density of 16.63 mA cm−2 at 2.2 VRHE, which is 277.2 times of n-Si and 1.92 times of Si/TiO2/Cu(dcbpy) at the same condition. This result indicates that p-n heterojunction accelerates the photogenerated holes transfer from Si to the electrocatalyst of Cu(dcbpy) to achieve a high water-splitting efficiency. This work provides an approach to designing efficient Si-based photoanodes through nanostructure-heterojunction interface engineering and molecular catalyst modification.

Self-Powered Hydrogen Production with Improved Energy Efficiency via Polysulfides Redox.

In the pursuit of efficient solar-driven electrocatalytic water splitting for hydrogen production, the intrinsic challenges posed by the sluggish kinetics of anodic oxygen evolution and intermittent sunlight have prompted the need for innovative energy systems. Here, we introduce an approach by coupling the polysulfides oxidation reaction with the hydrogen evolution reaction for energy-saving H2 production, which could be powered by an aqueous zinc-polysulfides battery to construct a self-powered energy system. This unusual hybrid water electrolyzer achieves 300 mA cm-2 at a low cell voltage of 1.14 V, saving electricity consumption by 100.4% from 5.47 to 2.73 kWh per m3 H2 compared to traditional overall water splitting. Benefiting from the favorable reaction kinetics of polysulfides oxidation/reduction, the aqueous zinc-polysulfides battery exhibits an energy efficiency of approximately 89% at 1.0 mA cm-2. Specially, the zinc-polysulfide battery effectively stores intermittent solar energy as chemical energy during light reaction by solar cells. Under an unassisted light reaction, the batteries could release energy to drive H2 production through a hybrid water electrolyzer for uninterrupted hydrogen production. Therefore, the aim of simultaneously generating H2 and eliminating the restrictions of intermittent sunlight is realized by combining the merits of polysulfides redox, an aqueous metal-polysulfide battery, and solar cells. We believe that this concept and utilization of polysulfides redox will inspire further fascinating attempts for the development of sustainable energy via electrocatalytic reactions.

3D Cellular Solar Crystallizer for Stable and Ultra-Efficient High-Salinity Wastewater Treatment.

Recent developed interfacial solar brine crystallizers, which employ solar-driven water evaporation for salts crystallization from the near-saturation brine to achieve zero liquid discharge (ZLD) brine treatment, are promising due to their excellent energy efficiency and sustainability. However, most existing interfacial solar crystallizers are only tested using NaCl solution and failed to maintain high evaporation capability when treating real seawater due to the scaling problem caused by the crystallization of high-valent cations. Herein, an artificial tree solar crystallizer (ATSC) with a multi-branched and interconnected open-cell cellular structure that significantly increased evaporation surface is rationally designed, achieving an ultra-high evaporation rate (2.30kgm-2 h-1 during 2h exposure) and high energy efficiency (128%) in concentrated real seawater. The unit cell design of ATSC promoted salt crystallization on the outer frame rather than the inner voids, ensuring that salt crystallization does not affect the continuous transport of brine through the pores inside the unit cell, thus ATSC can maintain a stable evaporation rate of 1.94kgm-2 h-1 on average in concentrated seawater for 80h continuous exposure. The design concept of ATSC represents a major step forward toward ZLD treatment of high-salinity brine in many industrial processes is believed.

PH controlled synthesis and photoelectrochemical kinetics of bismuth molybdate (Bi2MoO6) nanoplates as photoanodes for solar-driven water splitting

pH controlled synthesis and photoelectrochemical kinetics of bismuth molybdate (Bi2MoO6) nanoplates as photoanodes for solar-driven water splitting

S-scheme heterojunction and dual co-catalysts on carbonized paper for biphase interface photocatalytic hydrogen production from water

Solar-driven water splitting by photocatalysts is considered a cost-effective and environmental-friendly way to produce hydrogen fuel. However, the efficiency of hydrogen production in photocatalysis systems is still low due to the inefficient light absorption, photogenerated carrier recombination, and sluggish reaction kinetics. Here, we design and synthesize a composite carbonized paper with Co3O4/Fe2O3/g-C3N4/Au loaded on carbonized fiber (CF) by layer-by-layer assembly. Fe2O3 and g-C3N4 form an S-scheme heterojunction for enhanced interfacial charge separation. The spatially separated Co3O4 and Au co-catalysts capture photogenerated carriers and inhibit surface recombination for enhancing oxidation and reduction kinetics. In addition, composite carbonized paper floats on the water surface to form a solid-gas biphase photocatalytic interface (photothermal-generated steam/composite carbonized paper/hydrogen) with the help of the photothermal effect of composite carbonized paper. This biphase photocatalytic interface effectively reduces the transmission resistance of hydrogen and the adsorption barrier of water molecules. The CF/Co3O4/Fe2O3/g-C3N4/Au composite paper exhibits an impressive hydrogen production rate up to 78,561.51 μmol h−1 g−1. Stable loading of Co3O4/Fe2O3/g-C3N4/Au in composite paper contributes to the photocatalytic cycle. The hydrogen evolution rate in the third cycle remains 96.5 %. This work demonstrates that the combination of S-scheme heterojunction, spatially separated co-catalysts, and biphase photocatalytic interface can be a promising strategy for efficient photocatalytic platforms for solar hydrogen production.

Guar Gum-Based Macroporous Hygroscopic Polymer for Efficient Atmospheric Water Harvesting.

Solar-driven atmospheric water harvesting technology has the advantage of not being limited by geography and has great potential in solving the freshwater crisis. Here, we first propose a purely natural and degradable superhydrophilic composite macroporous hygroscopic material by applying guar gum (GG) to atmospheric water harvesting. The material consists of GG-cellulose nanofibers (CNFs) as a porous substrate material, limiting the hygroscopic factor lithium chloride (LiCl) in its three-dimensional (3D) network structure, and carbon nanotubes (CNTs) play a photothermal conversion role. The composite material has a high light absorption rate of more than 95%, and the macroporous structure (20-60 μm) allows for rapid adsorption/desorption kinetics. At 35 °C and 90% relative humidity (RH), the moisture absorption capacity is as high as 1.94 g/g. Under 100 mW/cm2 irradiation, the absorbed water is almost completely desorbed within 3 h, and the water harvesting performance is stable in 10 cycles. Moreover, liquid water was successfully collected in an actual outdoor experiment. This work demonstrates the great potential of biomass materials in the field of atmospheric water collection and provides more opportunities for various energy and sustainable applications in the future.

MOF-on-MOF-Derived Ultrafine Fe2P-Co2P Heterostructures for High-Efficiency and Durable Anion Exchange Membrane Water Electrolyzers.

The alkaline hydrogen evolution reaction (HER) in an anion exchange membrane water electrolyzer (AEMWE) is considered to be a promising approach for large-scale industrial hydrogen production. Nevertheless, it is severely hampered by the inability to operate tolerable HER catalysts consistently under low overpotentials at ampere-level current densities. Here, we develop a universal ligand-exchange (MOF-on-MOF) modulation strategy to synthesize ultrafine Fe2P and Co2P nanoparticles, which are well anchored on N and P dual-doped carbon porous nanosheets (Fe2P-Co2P/NPC). In addition, benefiting from the downshift of the d-band center and the interfacial Co-P-Fe bridging, the electron-rich P site is triggered, which induces the redistribution of electron density and the swapping of active centers, lowering the energy barrier of the HER. As a result, the Fe2P-Co2P/NPC catalyst only requires a low overpotential of 175 mV to achieve a current density of 1000 mA cm-2. The solar-driven water electrolysis system presents a record-setting and stable solar-to-hydrogen conversion efficiency of 20.36%. Crucially, the catalyst could stably operate at 1000 mA cm-2 over 1000 h in a practical AEMWE at an estimated cost of US$0.79 per kilogram of H2, which achieves the target (US$2 per kg of H2) set by the U.S. Department of Energy (DOE).

Efficient Solar-Driven Water Splitting Enabled by Perovskite Photovoltaics and a Halogen-Modulated Metal-Organic Framework Electrocatalyst.

Solar-driven water splitting powered by photovoltaics enables efficient storage of solar energy in the form of hydrogen fuel. In this work, we demonstrate efficient solar-to-hydrogen conversion using perovskite (PVK) tandem photovoltaics and a halogen-modulated metal-organic framework (MOF) electrocatalyst. By substituting tetrafluoroterephthalate (TFBDC) for terephthalic (BDC) ligands in a nickel-based MOF, we achieve a 152 mV improvement in oxygen evolution reaction (OER) overpotential at 10 mA·cm2. Through X-ray photoelectron spectroscopy (XPS), X-ray adsorption structure (XAS) analysis, theoretical simulation, and electrochemical results, we demonstrated that the introduction of fluorine atoms enhanced the intrinsic activity of Ni sites as well as the transfer property and accessibility of the MOF. Using this electrocatalyst in a bias-free photovoltaic electrochemical (PV-EC) system with a PVK/organic tandem solar cell, we achieve 6.75% solar-to-hydrogen efficiency (ηSTH). We also paired the electrocatalyst with a PVK photovoltaic module to drive water splitting at 206.7 mA with ηSTH of 10.17%.

Self-activated superhydrophilic green ZnIn2S4 realizing solar-driven overall water splitting: close-to-unity stability for a full daytime

Engineering an efficient semiconductor to sustainably produce green hydrogen via solar-driven water splitting is one of the cutting-edge strategies for carbon-neutral energy ecosystem. Herein, a superhydrophilic green hollow ZnIn2S4 (gZIS) was fabricated to realize unassisted photocatalytic overall water splitting. The hollow hierarchical framework benefits exposure of intrinsically active facets and activates inert basal planes. The superhydrophilic nature of gZIS promotes intense surface water molecule interactions. The presence of vacancies within gZIS facilitates photon energy utilization and charge transfer. Systematic theoretical computations signify the defect-induced charge redistribution of gZIS enhancing water activation and reducing surface kinetic barriers. Ultimately, the gZIS could drive photocatalytic pure water splitting by retaining close-to-unity stability for a full daytime reaction with performance comparable to other complex sulfide-based materials. This work reports a self-activated, single-component cocatalyst-free gZIS with great exploration value, potentially providing a state-of-the-art design and innovative aperture for efficient solar-driven hydrogen production to achieve carbon-neutrality.