Highly Efficient Solar‐Driven Carbon Dioxide Reduction on Molybdenum Disulfide Catalyst Using Choline Chloride‐Based Electrolyte

Conversion of CO₂ to energy‐rich chemicals using renewable energy is of much interest to close the anthropogenic carbon cycle. However, the current photoelectrochemical systems are still far from being practically feasible. Here the successful demonstration of a continuous, energy efficient, and scalable solar‐driven CO₂ reduction process based on earth‐abundant molybdenum disulfide (MoS₂) catalyst, which works in synergy with an inexpensive hybrid electrolyte of choline chloride (a common food additive for livestock) and potassium hydroxide (KOH) is reported. The CO₂ saturated hybrid electrolyte utilized in this study also acts as a buffer solution (pH ≈ 7.6) to adjust pH during the reactions. This study reveals that this system can efficiently convert CO₂ to CO with solar‐to‐fuel and catalytic conversion efficiencies of 23% and 83%, respectively. Using density functional theory calculations, a new reaction mechanism in which the water molecules near the MoS₂ cathode act as proton donors to facilitate the CO₂ reduction process by MoS₂ catalyst is proposed. This demonstration of a continuous, cost‐effective, and energy efficient solar driven CO₂ conversion process is a key step toward the industrialization of this technology.     

Metal‐Free Artificial Photosynthesis of Carbon Monoxide Using N‐Doped ZnTe Nanorod Photocathode Decorated with N‐Doped Carbon Electrocatalyst Layer

An artificial photosynthesis system based on N‐doped ZnTe nanorods decorated with an N‐doped carbon electrocatalyst layer is fabricated via an all‐solution process for the selective conversion of CO₂ to CO. Substitutional N‐doping into the ZnTe lattice decreases the bandgap slightly and improves the charge transfer characteristics, leading to enhanced photoelectrochemical activity. Remarkable N‐doping effects are also demonstrated by the N‐doped carbon layer that promotes selective CO₂‐to‐CO conversion instead of undesired water‐to‐H₂ reduction by providing active sites for CO₂ adsorption and activation, even in the absence of metallic redox centers. The photocathode shows promising performance in photocurrent generation (?1.21 mA cm^?2 at ?0.11 V_RHE), CO selectivity (dominant CO production of ≈72%), minor H₂ reduction (≈20%), and stability (corrosion suppression). The metal‐free electrocatalyst/photocatalyst combination prepared via a cost‐effective solution process exhibits high performance due to synergistic effects between them, and thus may find application in practical solar fuel production.     

Modifying La0.6Sr0.4MnO3 Perovskites with Cr Incorporation for Fast Isothermal CO2‐Splitting Kinetics in Solar‐Driven Thermochemical Cycles

Perovskites are promising oxygen carriers for solar‐driven thermochemical fuel production due to higher oxygen exchange capacity. Despite their higher fuel yield capacity, La_0.6Sr_0.4MnO₃ perovskite materials present slow CO₂‐splitting kinetics compared with state‐of‐the‐art CeO₂. In order to improve the CO production rates, the incorporation of Cr in La_0.6Sr_0.4MnO₃ is explored based on thermodynamic calculations that suggest an enhanced driving force toward CO₂ splitting at high temperatures for La_0.6Sr_0.4Cr_xMn_1?xO₃ perovskites. Here, reported is a threefold faster CO fuel production for La_0.6Sr_0.4Cr_0.85Mn_0.15O₃ compared to conventional La_0.6Sr_0.4MnO₃, and twofold faster than CeO₂ under isothermal redox cycling at 1400 °C, and high stability upon long‐term cycling without any evidence of microstructural degradation. The findings suggest that with the proper design in terms of transition metal ion doping, it is possible to adjust perovskite compositions and reactor conditions for improved solar‐to‐fuel thermochemical production under nonconventional solar‐driven thermochemical cycling schemes such as the here presented near isothermal operation.     

Metal Halide Perovskites for Solar‐to‐Chemical Fuel Conversion

This review article presents and discusses the recent progress made in the stabilization, protection, improvement, and design of halide perovskite‐based photocatalysts, photoelectrodes, and devices for solar‐to‐chemical fuel conversion. With the target of water splitting, hydrogen iodide splitting, and CO₂ reduction reactions, the strategies established for halide perovskites used in photocatalytic particle‐suspension systems, photoelectrode thin‐film systems, and photovoltaic‐(photo)electrocatalysis tandem systems are organized and introduced. Moreover, recent achievements in discovering new and stable halide perovskite materials, developing protective and functional shells and layers, designing proper reaction solution systems, and tandem device configurations are emphasized and discussed. Perspectives on the future design of halide perovskite materials and devices for solar‐to‐chemical fuel conversion are provided. This review may serve as a guide for researchers interested in utilizing halide perovskite materials for solar‐to‐chemical fuel conversion.     

Considerations in the Design of Materials for Solar‐Driven Fuel Production Using Metal‐Oxide Thermochemical Cycles

With demand for energy increasing worldwide and an ever‐stronger case building for anthropogenic climate change, the need for carbon‐neutral fuels is becoming an imperative. Extensive transportation infrastructure based on liquid hydrocarbon fuels motivates development of processes using solar energy to convert CO₂ and H₂O to fuel precursors such as synthesis gas. Here, perspectives concerning the use of solar‐driven thermochemical cycles using metal oxides to produce fuel precursors are given and, in particular, the important relationship between reactor design and material selection is discussed. Considering both a detailed thermodynamic analysis and factors such as reaction kinetics, volatility, and phase stability, an integrated analytical approach that facilitates material design is presented. These concepts are illustrated using three oxide materials currently receiving considerable attention: metal‐substituted ferrites, ceria, and doped cerias. Although none of these materials is “ideal,” the tradeoffs made in selecting any one of them are clearly indicated, providing a starting point for assessing the feasibility of alternative materials developed in the future.     

Electrochemical CO2 Reduction with Atomic Iron‐Dispersed on Nitrogen‐Doped Graphene

Electrochemical reduction of CO₂ provides an opportunity to reach a carbon‐neutral energy recycling regime, in which CO₂ emissions from fuel use are collected and converted back to fuels. The reduction of CO₂ to CO is the first step toward the synthesis of more complex carbon‐based fuels and chemicals. Therefore, understanding this step is crucial for the development of high‐performance electrocatalyst for CO₂ conversion to higher order products such as hydrocarbons. Here, atomic iron dispersed on nitrogen‐doped graphene (Fe/NG) is synthesized as an efficient electrocatalyst for CO₂ reduction to CO. Fe/NG has a low reduction overpotential with high Faradic efficiency up to 80%. The existence of nitrogen‐confined atomic Fe moieties on the nitrogen‐doped graphene layer is confirmed by aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy and X‐ray absorption fine structure analysis. The Fe/NG catalysts provide an ideal platform for comparative studies of the effect of the catalytic center on the electrocatalytic performance. The CO₂ reduction reaction mechanism on atomic Fe surrounded by four N atoms (Fe–N₄) embedded in nitrogen‐doped graphene is further investigated through density functional theory calculations, revealing a possible promotional effect of nitrogen doping on graphene.     

Continuous 3D Titanium Nitride Nanoshell Structure for Solar‐Driven Unbiased Biocatalytic CO2 Reduction

Z‐scheme‐inspired tandem photoelectrochemical (PEC) cells have received attention as a sustainable platform for solar‐driven CO₂ reduction. Here, continuously 3D‐structured, electrically conductive titanium nitride nanoshells (3D TiN) for biocatalytic CO₂‐to‐formate conversion in a bias‐free tandem PEC system are reported. The 3D TiN exhibits a periodically porous network with high porosity (92.1%) and conductivity (6.72 × 10⁴ S m^?1), which allows for high enzyme loading and direct electron transfer (DET) to the immobilized enzyme. It is found that the W‐containing formate dehydrogenase from Clostridium ljungdahlii (ClFDH) on the 3D TiN nanoshell is electrically activated through DET for CO₂ reduction. At a low overpotential of 40 mV, the 3D TiN‐ClFDH stably converts CO₂ to formate at a rate of 0.34 µmol h^?1 cm^?2 and a faradaic efficiency (FE) of 93.5%. Compared to a flat TiN‐ClFDH, the 3D TiN‐ClFDH shows a 58 times higher formate production rate (1.74 µmol h^?1 cm^?2) at 240 mV of overpotential. Lastly, a bias‐free biocatalytic tandem PEC cell that converted CO₂ to formate at an average rate of 0.78 µmol h^?1 and an FE of 77.3% only using solar energy and water is successfully assembled.     

Change in terrestrial ecosystem water‐use efficiency over the last three decades

Defined as the ratio between gross primary productivity (GPP) and evapotranspiration (ET), ecosystem‐scale water‐use efficiency (EWUE) is an indicator of the adjustment of vegetation photosynthesis to water loss. The processes controlling EWUE are complex and reflect both a slow evolution of plants and plant communities as well as fast adjustments of ecosystem functioning to changes of limiting resources. In this study, we investigated EWUE trends from 1982 to 2008 using data‐driven models derived from satellite observations and process‐oriented carbon cycle models. Our findings suggest positive EWUE trends of 0.0056, 0.0007 and 0.0001 g C m^?2 mm^?1 yr^?1 under the single effect of rising CO₂ (‘CO₂’), climate change (‘CLIM’) and nitrogen deposition (‘NDEP’), respectively. Global patterns of EWUE trends under different scenarios suggest that (i) EWUE‐CO₂ shows global increases, (ii) EWUE‐CLIM increases in mainly high latitudes and decreases at middle and low latitudes, (iii) EWUE‐NDEP displays slight increasing trends except in west Siberia, eastern Europe, parts of North America and central Amazonia. The data‐driven MTE model, however, shows a slight decline of EWUE during the same period (?0.0005 g C m^?2 mm^?1 yr^?1), which differs from process‐model (0.0064 g C m^?2 mm^?1 yr^?1) simulations with all drivers taken into account. We attribute this discrepancy to the fact that the nonmodeled physiological effects of elevated CO₂ reducing stomatal conductance and transpiration (TR) in the MTE model. Partial correlation analysis between EWUE and climate drivers shows similar responses to climatic variables with the data‐driven model and the process‐oriented models across different ecosystems. Change in water‐use efficiency defined from transpiration‐based WUE_t (GPP/TR) and inherent water‐use efficiency (IWUE_t, GPP×VPD/TR) in response to rising CO₂, climate change, and nitrogen deposition are also discussed. Our analyses will facilitate mechanistic understanding of the carbon–water interactions over terrestrial ecosystems under global change.     

The Effects of Catalyst Layer Deposition Methodology on Electrode Performance

The catalyst layer of the cathode is arguably the most critical component of low‐temperature fuel cells and carbon dioxide (CO₂) electrolysis cells because their performance is typically limited by slow oxygen (O₂) and CO₂ reduction kinetics. While significant efforts have focused on developing cathode catalysts with improved activity and stability, fewer efforts have focused on engineering the catalyst layer structure to maximize catalyst utilization and overall electrode and system performance. Here, we study the performance of cathodes for O₂ reduction and CO₂ reduction as a function of three common catalyst layer preparation methods: hand‐painting, air‐brushing, and screen‐printing. We employed ex‐situ X‐ray micro‐computed tomography (MicroCT) to visualize the catalyst layer structure and established data processing procedures to quantify catalyst uniformity. By coupling structural analysis with in‐situ electrochemical characterization, we directly correlate variation in catalyst layer morphology to electrode performance. MicroCT and SEM analyses indicate that, as expected, more uniform catalyst distribution and less particle agglomeration, lead to better performance. Most importantly, the analyses reported here allow for the observed differences over a large geometric volume as a function of preparation methods to be quantified and explained for the first time. Depositing catalyst layers via a fully‐automated air‐brushing method led to a 56% improvement in fuel cell performance and a significant reduction in electrode‐to‐electrode variability. Furthermore, air‐brushing catalyst layers for CO₂ reduction led to a 3‐fold increase in partial CO current density and enhanced product selectivity (94% CO) at similar cathode potential but a 10‐fold decrease in catalyst loading as compared to previous reports.     

Tunable and Efficient Tin Modified Nitrogen‐Doped Carbon Nanofibers for Electrochemical Reduction of Aqueous Carbon Dioxide

Efficient and selective earth‐abundant catalysts are highly desirable to drive the electrochemical conversion of CO₂ into value‐added chemicals. In this work, a low‐cost Sn modified N‐doped carbon nanofiber hybrid catalyst is developed for switchable CO₂ electroreduction in aqueous medium via a straightforward electrospinning technique coupled with a pyrolysis process. The electrocatalytic performance can be tuned by the structure of Sn species on the N‐doped carbon nanofibers. Sn nanoparticles drive efficient formate formation with a high current density of 11 mA cm^?2 and a faradaic efficiency of 62% at a moderate overpotential of 690 mV. Atomically dispersed Sn species promote conversion of CO₂ to CO with a high faradaic efficiency of 91% at a low overpotential of 490 mV. The interaction between Sn species and pyridinic‐N may play an important role in tuning the catalytic activity and selectivity of these two materials.     

Surface‐Plasmon‐Assisted Photoelectrochemical Reduction of CO2 and NO3− on Nanostructured Silver Electrodes

Electrochemical reduction of carbon dioxide (CO₂) typically suffers from low selectivity and poor reaction rates that necessitate high overpotentials, which impede its possible application for CO₂ capture, sequestration, or carbon‐based fuel production. New strategies to address these issues include the utilization of photoexcited charge carriers to overcome activation barriers for reactions that produce desirable products. This study demonstrates surface‐plasmon‐enhanced photoelectrochemical reduction of CO₂ and nitrate (NO₃^?) on silver nanostructured electrodes. The observed photocurrent likely originates from a resonant charge transfer between the photogenerated plasmonic hot electrons and the lowest unoccupied molecular orbital (MO) acceptor energy levels of adsorbed CO₂, NO₃^?, or their reductive intermediates. The observed differences in the resonant effects at the Ag electrode with respect to electrode potential and photon energy for CO₂ versus NO₃^? reduction suggest that plasmonic hot‐carriers interact selectively with specific MO acceptor energy levels of adsorbed surface species such as CO₂, NO₃^?, or their reductive intermediates. This unique plasmon‐assisted charge generation and transfer mechanism can be used to increase yield, efficiency, and selectivity of various photoelectrochemical processes.     

Edge‐Exposed Molybdenum Disulfide with N‐Doped Carbon Hybridization: A Hierarchical Hollow Electrocatalyst for Carbon Dioxide Reduction

Electrochemical CO₂ reduction (CO₂RR) is a promising technology to produce value‐added fuels and weaken the greenhouse effect. Plenty of efforts are devoted to exploring high‐efficiency electrocatalysts to tackle the issues that show poor intrinsic activity, low selectivity for target products, and short‐lived durability. Herein, density functional theory calculations are firstly utilized to demonstrate guidelines for design principles of electrocatalyst, maximum exposure of catalytic active sites for MoS₂ edges, and electron transfer from N‐doped carbon (NC) to MoS₂ edges. Based on the guidelines, a hierarchical hollow electrocatalyst comprised of edge‐exposed 2H MoS₂ hybridized with NC for CO₂RR is constructed. In situ atomic‐scale observation for catalyst growth is performed by using a specialized Si/SiN_x nanochip at a continuous temperature‐rise period, which reveals the growth mechanism. Abundant exposed edges of MoS₂ provide a large quantity of active centers, which leads to a low onset potential of ≈40 mV and a remarkable CO production rate of 34.31 mA cm^?2 with 92.68% of Faradaic efficiency at an overpotential of 590 mV. The long‐term stability shows negligible degradation for more than 24 h. This work provides fascinating insights into the construction of catalysts for efficient CO₂RR.     

A Delaminated Defect‐Rich ZrO2 Hierarchical Nanowire Photocathode for Efficient Photoelectrochemical Hydrogen Evolution

An efficient way to combat the energy crisis and the greenhouse gas effect of fossil fuels is the production of hydrogen fuel from solar‐driven water splitting reaction. Here, this study presents a p‐type ZrO₂ nanoplate‐decorated ZrO₂ nanowire photocathode with a high photoconversion efficiency that makes it potentially viable for commercial solar H₂ production. The composition of oxygen vacancy defects, low charge carrier transport property, and high specific surface area of these as‐grown hierarchical nanowires are further improved by an hydrofluoric acid (HF) treatment, which causes partial delamination and produces a thin amorphous ZrO₂ layer on the surface of the as‐grown nanostructured film. The presence of different types of oxygen vacancies (neutral, singly charged, and doubly charged defects) and their compositional correlation to the Zr^x+ oxidation states (4 > x > 2) are found to affect the charge transfer process, the p‐type conductivity, and the photocatalytic activity of the ZrO₂ nanostructured film. The resulting photocathode provides the highest overall photocurrent (?42.3 mA cm^?2 at 0 V vs reversible hydrogen electrode (RHE)) among all the photocathodes reported to date, and an outstanding 3.1% half‐cell solar‐to‐hydrogen conversion efficiency with a Faradaic efficiency of 97.8%. Even more remarkable is that the majority of the photocurrent (69%) is produced in the visible light region.     

Simultaneous Achieving of High Faradaic Efficiency and CO Partial Current Density for CO2 Reduction via Robust,Noble‐Metal‐Free Zn Nanosheets with Favorable Adsorption Energy

Electrocatalytic CO₂ reduction to fuels is considered a promising strategy for the sustainable carbon cycle. However, the improvement of the catalytic performance of CO₂ electrocatalysts still poses many challenges, especially achieving the large partial current density of product and high faradaic efficiency simultaneously, which are essential for future applications of the electrochemical CO₂ reduction reaction. In response, herein, an in situ porous Zn catalyst is prepared and exhibits high faradaic efficiency and large CO partial current density at the same time, benefiting from the porous architecture with increased exposure and accessibility of active sites. Furthermore, density functional theory calculations demonstrate that the high faradaic efficiency is attributed to the favorable adsorption energy of the key intermediate, which promotes CO₂ electroreduction to CO.     

Modeling Thermochemical Solar‐to‐Fuel Conversion: CALPHAD for Thermodynamic Assessment Studies of Perovskites,Exemplified for (La,Sr)MnO3

Two‐step solar thermochemical fuel production has the potential to reduce global greenhouse gas emissions and replace fossil fuels. The success of the technology relies on the development of materials with high thermochemical efficiency. Perovskites with the general structure ABO₃ have received much attention recently due to impressive fuel productivity and their amenability of substituting and doping both A‐ and B‐site. Despite the potential of perovskites for solar‐to‐fuel conversion, literature on their solar thermochemical efficiency is scarce and finding the best chemical composition and optimum operation conditions is unknown. For this purpose, this study suggests to use Computer Coupling of Phase Diagrams and Thermochemistry (CALPHAD) data libraries to access the relevant thermodynamic properties of perovskites. This work demonstrates the usefulness of employing CALPHAD data by a full thermodynamic study of the model case compositions of La_1–xSr_xMnO_3–δ. This study uses data on oxygen‐nonstoichiometry and heat capacity in the temperature range of 1073–1873 K relevant for solar‐to‐fuel. Unlike earlier thermodynamic assessments of perovskites that rely on a single literature source and a limited temperature range, the CALPHAD approach takes all available data in literature into consideration. Thermochemical equilibrium models of fuel yields are accompanied by validations toward experimental results in literature, and this study highlights the effects of strontium doping level on the efficiency.     

Atomic Fe‐Doped MOF‐Derived Carbon Polyhedrons with High Active‐Center Density and Ultra‐High Performance toward PEM Fuel Cells

A metalorganic gaseous doping approach for constructing nitrogen‐doped carbon polyhedron catalysts embedded with single Fe atoms is reported. The resulting catalysts are characterized using scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, and X‐ray absorption spectroscopy; for the optimal sample, calculated densities of Fe–N_x sites and active N sites reach 1.75812 × 10¹³ and 1.93693 × 10¹⁴ sites cm^‐2, respectively. Its oxygen reduction reaction half‐wave potential (0.864 V) is 50 mV higher than that of 20 wt% Pt/C catalyst in an alkaline medium and comparable to the latter (0.78 V vs 0.84 V) in an acidic medium, along with outstanding durability. More importantly, when used as a hydrogen–oxygen polymer electrolyte membrane fuel cell (PEMFC) cathode catalyst with a catalyst loading as low as 1 mg cm^‐2 (compared with a conventional loading of 4 mg cm^‐2), it exhibits a current density of 1100 mA cm^‐2 at 0.6 V and 637 mA cm^‐2 at 0.7 V, with a power density of 775 mW cm^‐2, or 0.775 kW g^–1 of catalyst. In a hydrogen–air PEMFC, current density reaches 650 mA cm^‐2 at 0.6 V and 350 mA cm^‐2 at 0.7 V, and the maximum power density is 463 mW cm^‐2, which makes it a promising candidate for cathode catalyst toward high‐performance PEMFCs.     

An Operando Mechanistic Evaluation of a Solar‐Rechargeable Sodium‐Ion Intercalation Battery

Solar‐intercalation batteries, which are able to both harvest and store solar energy within the electrodes, are a promising technology for the more efficient utilization of intermittent solar radiation. However, there is a lack of understanding on how the light‐induced intercalation reaction occurs within the electrode host lattice. Here, an in operando synchrotron X‐ray diffraction methodology is introduced, which allows for real‐time visualization of the structural evolution process within a solar‐intercalation battery host electrode lattice. Coupled with ex situ material characterization, direct correlations between the structural evolution of MoO₃ and the photo‐electrochemical responses of the solar‐intercalation batteries are established for the first time. MoO₃ is found to transform, via a two‐phase reaction mechanism, initially into a sodium bronze phase, Na_0.33MoO₃, followed by the formation of solid solutions, Na_xMoO₃ (0.33 < x < 1.1), on further photointercalation. Time‐resolved correlations with the measured voltages indicate that the two‐phase evolution reaction follows zeroth‐order kinetics. The insights achieved from this study can aid the development of more advanced photointercalation electrodes and solar batteries with greater performances.     

Biomass‐Derived 3D Carbon Aerogel with Carbon Shell‐Confined Binary Metallic Nanoparticles in CNTs as an Efficient Electrocatalyst for Microfluidic Direct Ethylene Glycol Fuel Cells

Flexible and 3D carbon aerogels (CAs) composed of carbon nanotubes (CNTs) with carbon shell‐confined binary palladium–nickel (Pd_x–Ni_y) nanocatalysts on carbon fibers (Pd_x–Ni_y/NSCNT/CA) have been developed through a facile chemical vapor deposition method. The 3D porous carbon network and the synergistic effect of carbon shell‐confined bimetal nanoparticles of rationally constructed aerogels facilitate enhanced electrocatalytic and antipoisoning activities toward ethylene glycol (EG) oxidation reaction compared to the commercial Pt/C catalyst. With the 3D morphological features and direct growth of Pd–Ni bimetallic nanoparticles encapsulated CNTs on carbon fibers, the Pd₅₂–Ni₄₈/NSCNT/CA delivers a maximum microfluidic direct ethylene glycol fuel cell (µDEGFC) power density and durability of, respectively, 62.8 mW cm^?2 and 60 h. The superior performance observed, with Pd₅₂–Ni₄₈/NSCNT/CA amongst the catalysts reported in the literature, opens an exciting research avenue towards powering next‐generation, portable electronics.     

Superior CO2 Adsorption Capacity on N‐doped,High‐Surface‐Area,Microporous Carbons Templated from Zeolite

Zeolite‐templated, high‐surface‐area, microporous, N‐doped carbons exhibit the highest CO₂ uptake capacity recorded to date for any carbon material and one of the highest for any inorganic or organic porous material of up to 6.9 mmol g^?1 at 273 K and ambient pressure and 4.4 mmol g^?1 at ambient temperature and pressure, along with an initial CO₂ adsorption energy of 36 kJ mol^?1 at lower coverage and 20 kJ mol^?1 at higher CO₂ coverage. Combined with their ease of preparation, excellent recyclability and regeneration stability, and high selectivity for CO₂, the N‐doped zeolite‐templated carbons are amongst the most promising solid‐state absorbents reported so far for CO₂ capture and storage.     

Solar‐to‐Hydrogen Energy Conversion Based on Water Splitting

Artificial photosynthesis provides a blueprint to harvest solar energy to sustain the future energy demands. Solar‐driven water splitting, converting solar energy into hydrogen energy, is the prototype of photosynthesis. Various systems have been designed and evaluated to understand the reaction pathways and/or to meet the requirements of potential applications. In solar‐to‐hydrogen conversion, electrocatalytic hydrogen and oxygen evolution reactions are key research areas that are meaningful both theoretically and practically. To utilize hydrogen energy, fuel cell technology has been extensively investigated because of its high efficiency in releasing chemical energy. In this review, general concepts of the photosynthesis in green plants are discussed, different strategies for the light‐driven water splitting proposed in laboratories are introduced, the progress of electrocatalytic hydrogen and oxygen evolution reactions are reviewed, and finally, the reactions in hydrogen fuel cells are briefly discussed. Overall, the mass and energy circulation in the solar‐hydrogen‐electricity circle are delineated. The authors conclude that attention from scientists and engineers of relevant research areas is still highly needed to eliminate the wide disparity between the aspirations and realities of artificial photosynthesis.