Catalytic Reduction Of CO2 Research Articles

Role-Specialized Division of Labor in CO2 Reduction with Doubly-Functionalized Iron Porphyrin Atropisomers.

In enzymes, the active site residues function differently to promote chemical reactions. Such a role-specialized division of labor has been rarely realized by synthetic catalysts. We report herein on catalytic CO2 reduction with Fe porphyrins decorated with two cationic N,N,N-trimethylbenzylamine groups in cis- or trans-arrangement. The cis-isomer outperforms the trans-isomer and reaches a TOFmax of 4.4×105 s-1 in acetonitrile using phenol proton source. Theoretical studies revealed that the two cationic units in the cis-isomer are more effective than a single cationic unit to improve the CO2 binding, and more importantly, they function differently but cooperatively to promote the C-O bond cleavage: one interacts with the CO2 -adduct, while the other one interacts with the phenol molecule through electrostatic interactions. This work therefore presents a significant example of synthetic catalysts, which boost chemical reactions using a role-specialized strategy for substrate activation.

Role‐Specialized Division of Labor in CO2 Reduction with Doubly‐Functionalized Iron Porphyrin Atropisomers

AbstractIn enzymes, the active site residues function differently to promote chemical reactions. Such a role‐specialized division of labor has been rarely realized by synthetic catalysts. We report herein on catalytic CO2 reduction with Fe porphyrins decorated with two cationic N,N,N‐trimethylbenzylamine groups in cis‐ or trans‐arrangement. The cis‐isomer outperforms the trans‐isomer and reaches a TOFmax of 4.4×105 s−1 in acetonitrile using phenol proton source. Theoretical studies revealed that the two cationic units in the cis‐isomer are more effective than a single cationic unit to improve the CO2 binding, and more importantly, they function differently but cooperatively to promote the C−O bond cleavage: one interacts with the CO2‐adduct, while the other one interacts with the phenol molecule through electrostatic interactions. This work therefore presents a significant example of synthetic catalysts, which boost chemical reactions using a role‐specialized strategy for substrate activation.

Breaking the intrinsic activity barriers of perovskite oxides photocatalysts for catalytic CO2 reduction via piezoelectric polarization

Breaking the limitations of the intrinsic redox potential of perovskite oxides photocatalysts for catalytic CO2 reduction remains a big challenge. Here we report a new process to achieve the durability yet efficient CO2 reduction activity of various perovskite oxides (BiFeO3, LaFeO3 and LaNiO3) with an inactive CO2 photo-reduction ability via piezoelectrically polarization. Taking BiFeO3 (BFO) as a representative sample, the band tilting and structure compression of BFO reach the redox potential of CO2 reduction and build a piezoelectric field for CO2 adsorption and activation by introducing vibration energy, inducing a piezoelectric catalytic CO2 reduction process. Continued ultrasonic vibration with BFO achieves durability CO2 reduction to high production rates of CH4 (17.9 µmol g−1 h−1) and CO (28.7 µmol g−1 h−1), respectively. This crucial feature highlights the feasibility of piezoelectric catalysis for CO2 conversion by utilizing mechanical energy, which can break the limitation of intrinsic redox properties of the perovskite oxides.

Synergetic enhancement of activity and selectivity for reverse water gas shift reaction on Pt-Re/SiO2 catalysts

Catalytic reduction of CO2 with renewable H2 to CO via the reverse water gas shift (RWGS) reaction is an attractive approach to recycle CO2 and control net emission of CO2 to atmosphere. However, low activity and high CH4 selectivity at low temperatures limited the practical implementation of the reaction. Herein, Pt-Re/SiO2 catalysts with varying amount of Re were prepared with co-impregnation and tested for the RWGS reaction. Characterization results indicated that the oxophilic ReOx (0 ≤ x ≤ 3.5) located in close proximity to Pt particle, modified the surface of Pt by both partial coverage and electronic interaction, resulting in the reduced number of sites for and weakened strength of CO adsorption. At 400 °C, the turnover frequency (2.30 s−1) on the optimal Pt-Re/SiO2 catalyst (Pt/Re = 1.91) is 3.9 times higher than that on Pt/SiO2 under differential conditions, and the apparent activation energy is lowered. In contrast to Re/SiO2 which produces significant amount of CH4, the CO selectivity on Pt-Re/SiO2 maintained > 96.2 % under integral conditions. Reaction order analysis revealed that Pt facilitates H2 activation whereas the oxophilic ReOx enhances CO2 adsorption and activation. The perimeter sites at the Pt/ReOx interface with a balanced hydrogenation and C-O cleavage properties synergistically improve the RWGS activity while inhibiting CH4 production.

Selective CO2 reduction to methane catalyzed by mesoporous Ru-Fe3O4/CeOx-SiO2 in a fixed bed flow reactor

Development of a robust catalyst for selective reduction of CO2 directly into hydrocarbon fuels is very challenging from both energy and environmental perspectives as it offers a renewable and green route for the production of fuels. Herein, we report a novel catalyst synthesized via excess solution impregnation of Ru and Fe3O4 nanoparticles (NPs) on ceria promoted mesoporous silica SBA-15 support. The selective catalytic reduction of CO2 to methane was carried out in the presence of H2 over novel Ru-Fe3O4/CeOx-SiO2 (Ce3+/Ce4+, x=1.64) catalyst in a fixed bed reactor. The CO2 conversion was found to be 82% at 0.25 wt% ruthenium loading, 2.5 wt% iron loading, 575 K temperature, 20 bar pressure, 3000 mLg−1h−1 gas hour space velocity and H2 to CO2 mole ratio of 5:1. The close contact between ruthenium and Fe3O4 nanoparticles facilitated the reduction of CO2 through hydrogen spill-over effect at lower temperature, whereas ceria NPs acted as a promoter for this reduction reaction. The catalysts were characterized thoroughly using physicochemical techniques such as CO chemisorption, BET, TPR, TPD, XRD, SEM, HR- TEM, ICP-AES and XPS analyses. High surface area and large mesopores of silica support facilitated the fine dispersion of the active catalytic sites and oxygen vacancy as supported from the DFT study on the catalytic activity. Optimal process conditions could render much higher CO2 conversion efficacy for selective methane synthesis in comparison with previous investigations.

Surface Modification of Three-Dimensional Au Coated Polymer Electrodes for Electrochemical Reduction of CO2

Electrochemical reduction of CO2 (CO2R) into chemical and fuels has found its place among scientists in the past decade as a promising field to invest in for moving towards a greener future. However, finding catalysts for CO2R has been a real challenge for researchers. The four main requirements for a good CO2R catalyst performance include activity, selectivity, stability, and low cost. Furthermore, as catalysis is a surface based process, achieving high catalytically active surface areas exposed to CO2 while the conversion process is occurring is important.The type of transition metal catalyst and the exposed surface facets used for CO2 reduction plays a role on the activity and selectivity towards different reaction products. Furthermore, tuning the 3-dimensional structure of CO2R electrodes enables control of the local reaction environment that can impact overall catalytic performance.1 In this work, we control the 3-dimensional structure of an Au catalyst coated on a polymeric-based substrate, along with investigating the impact of surface decoration of metal adatoms.The coating of Au on the polymer substrate was accomplished following a previously developed electroless deposition method.2 CO2R was carried out in a custom designed three electrode cell reported previously3 with a flow of CO2 maintained over a 1 h chronoamperometry electrolysis process. The counter electrode was Pt foil and 0.1 M KHCO3 was used as the electrolyte.The modified surface showed an almost 5 times higher peak in its cyclic voltammetry (CV) in compare to the plain surface. This means that the actual active surface area of the modified surface sample is almost 5 times higher the plain sample (demonstrated in Figure 1a). This significantly affects the CO2R performance of these surfaces. Figure 1b depicts the activity of the modified three-dimensional electrode surface and the two-dimensional plain surface as a function of electrode potential. By decorating these electrodes with other metal species at the surface we observed interesting activity and selectivity trends that arise due to synergistic interactions between the two metal species and modified transport properties due to the three-dimensionality of the polymer supported electrodes. In this presentation we will discuss these reactivity trends and provide insight into the activity and selectivity observed, supported by detailed structural analyses and supplementary measurements. Figure 1. (a) CV of a plain and modified surface of Au in 2.25 M of H2SO4; the counter electrode was Pt foil and the scan rate was 50 mV/s. (b) Activity (current density vs. different electrode potentials) of both the three-dimensional modified and two-dimensional plain surfaces. References Hall, A. S.; Yoon, Y.; Wuttig, A.; Surendranath, Y., Mesostructure-Induced Selectivity in CO2 Reduction Catalysis. Journal of the American Chemical Society 2015, 137 (47), 14834-14837.Gabardo, C. M.; Adams-McGavin, R. C.; Fung, B. C.; Mahoney, E. J.; Fang, Q.; Soleymani, L., Rapid prototyping of all-solution-processed multi-lengthscale electrodes using polymer-induced thin film wrinkling. Scientific Reports 2017, 7 (1), 1-9.Kuhl, K. P.; Cave, E. R.; Abram, D. N.; Jaramillo, T. F., New insights into the electrochemical reduction of carbon dioxide on metallic copper surfaces. Energy & Environmental Science 2012, 5 (5), 7050-7059. Figure 1

Exploring the reduction reaction mechanism of CO2 on graphene-supported metal dimers using density functional theory

The reduction of CO2 into clean energy through electro catalytic technology provides a promising solution to alleviate energy shortages. In this paper, the graphitised material-supported metal dimer used for electro catalytic reduction of CO2 was proposed, and the reduction reaction mechanism was explored by density functional theory. The results indicate that the hydrogenation reduction of CO2 tends to occur preferentially, and it was found that improving the stability of catalyst structure can reduce the free energy of reaction and improve the adsorption effect of reactants, which significantly increase the conversion efficiency of CO2. The activation of CO2 on the catalyst surface is closely related to the binding of O atoms on the metal sites, the main reduction products and their reaction pathways were clarified. The reduction over potentials of CuCo-C, CuRh-C, CuZn-C and ZnCu-C were 0.915, 0.820, 0.774, and 0.354 V, respectively, thus ZnCu-C had a lower reduction over potential and higher catalytic efficiency.

Templating Bicarbonate in the Second Coordination Sphere Enhances Electrochemical CO2 Reduction Catalyzed by Iron Porphyrins.

Bicarbonate-based electrolytes are ubiquitous in aqueous electrochemical CO2 reduction, particularly in heterogenous catalysis, where they demonstrate improved catalytic performance relative to other buffers. In contrast, the presence of bicarbonate in organic electrolytes and its roles in homogeneous electrocatalysis remain underexplored. Here, we investigate the influence of bicarbonate on iron porphyrin-catalyzed electrochemical CO2 reduction. We show that bicarbonate is a viable proton donor in organic electrolyte (pKa = 20.8 in dimethyl sulfoxide) and that urea pendants in the second coordination sphere can be used to template bicarbonate in the vicinity of a molecular iron porphyrin catalyst. The templated binding of bicarbonate increases its acidity, resulting in a 1500-fold enhancement in catalytic rates relative to unmodified parent iron porphyrin. This work emphasizes the importance of bicarbonate speciation in wet organic electrolytes and establishes second-sphere bicarbonate templating as a design strategy to harness this adventitious acid and enhance CO2 reduction catalysis.

Phosphine–borane catalysts for CO2 activation and reduction: a computational study

CO2 conversion to value-added chemicals requires efficient catalytic CO2 reduction. Activation of CO2 using 14 phosphine–borane frustrated Lewis pair catalysts was done computationally using B3LYP-D3/6-31++G(d,p)/PCM/THF and M06-2X/6-311++G(d,p)/PCM/THF methods. We designed 14 catalysts, 12 of which exhibit better catalytic activity towards CO2 activation. Moreover, the catalytic mechanisms of compounds 12 and 4 were predicted, and they showed an efficient catalytic system for CO2 reduction to CO, HCHO and HCOOH. Catalysts 2, 3 and 4, with the same methylene linker, have activation energies of 20.5, 18.3 and 10.4 kcal/mol, respectively. This indicates that the catalytic activity of the compound is highly influenced by the ligand bound to borane and phosphine. Compound 4 with the CO2 activation energy of 10.4 kcal/mol is the most efficient catalyst for CO2 activation ever reported among phosphine–borane catalysts. The energy barriers for H2 activation with catalyst 12 (ΔG ‡ = 26.6 kcal/mol) and 4 (ΔG ‡ = 34.0 kcal/mol) are higher than the HCOOH releasing activation energy. The designed compounds will help to synthesise efficient metal-free phosphine–borane catalysts. Our results also indicate that phosphine–borane catalysts are promising candidates for CO2 reduction and direct hydrogenation.

Bioinspired Metalation of the Metal‐Organic Framework MIL‐125‐NH2 for Photocatalytic NADH Regeneration and Gas‐Liquid‐Solid Three‐Phase Enzymatic CO2 Reduction

AbstractCoenzyme NADH regeneration is crucial for sustained photoenzymatic catalysis of CO2 reduction. However, light‐driven NADH regeneration still suffers from the low regeneration efficiency and requires the use of a homogeneous Rh complex. Herein, a Rh complex‐based electron transfer unit was chemically attached onto the linker of the MIL‐125‐NH2. The coupling between the light‐harvesting iminopyridine unit and electron‐transferring Rh‐complex facilitated the photo‐induced electron transfer for the NADH regeneration with the yield of 66.4 % in 60 mins for 5 cycles. The formate dehydrogenase was further deposited onto the hydrophobic layer of the membrane by a reverse filtering technique, which forms the gas‐liquid‐solid reaction interface around the enzyme site. It gave an enhanced formic acid yield of 9.5 mM in 24 hours coupled with the in situ regenerated NADH. The work could shed light on the construction of integrated inorganic‐enzyme hybrid systems for artificial photosynthesis.

Bioinspired Metalation of the Metal-Organic Framework MIL-125-NH2 for Photocatalytic NADH Regeneration and Gas-Liquid-Solid Three-Phase Enzymatic CO2 Reduction.

Coenzyme NADH regeneration is crucial for sustained photoenzymatic catalysis of CO2 reduction. However, light-driven NADH regeneration still suffers from the low regeneration efficiency and requires the use of a homogeneous Rh complex. Herein, a Rh complex-based electron transfer unit was chemically attached onto the linker of the MIL-125-NH2 . The coupling between the light-harvesting iminopyridine unit and electron-transferring Rh-complex facilitated the photo-induced electron transfer for the NADH regeneration with the yield of 66.4 % in 60 mins for 5 cycles. The formate dehydrogenase was further deposited onto the hydrophobic layer of the membrane by a reverse filtering technique, which forms the gas-liquid-solid reaction interface around the enzyme site. It gave an enhanced formic acid yield of 9.5 mM in 24 hours coupled with the in situ regenerated NADH. The work could shed light on the construction of integrated inorganic-enzyme hybrid systems for artificial photosynthesis.

Direct Conversion of CO2 into Hydrocarbon Solar Fuels by a Synergistic Photothermal Catalysis

Photothermal coupling catalysis technology has been widely studied in recent years and may be a promising method for CO2 reduction. Photothermal coupling catalysis can improve chemical reaction rates and realize the controllability of reaction pathways and products, even in a relatively moderate reaction condition. It has inestimable value in the current energy and global environmental crisis. This review describes the application of photothermal catalysis in CO2 reduction from different aspects. Firstly, the definition and advantages of photothermal catalysis are briefly described. Then, different photothermal catalytic reductions of CO2 products and catalysts are introduced. Finally, several strategies to improve the activity of photothermal catalytic reduction of CO2 are described and we present our views on the future development and challenges of photothermal coupling. Ultimately, the purpose of this review is to bring more researchers’ attention to this promising technology and promote this technology in solar fuels and chemicals production, to realize the value of the technology and provide a better path for its development.

An effective Z-scheme hybrid photocatalyst based on zinc porphyrin derivative and anatase titanium dioxide microsphere for carbon dioxide reduction

Photocatalysis is considered as one of the most promising technologies to convert carbon dioxide (CO2) into high-valued chemicals. Herein, a novel hybrid photocatalyst for effectively catalyzing CO2 reduction reaction (CO2RR) is synthesized using zinc(II)-tetra-(4-pyridyl) porphyrin (ZnPy4) and MnOx-decorated anatase titanium dioxide (TiO2) microspheres (Mn/AMS) as raw materials. The resultant ZnPy4-Mn/AMS hybrid material exhibits excellent photocatalytic CO2RR performance with methane (CH4)/ carbon monoxide (CO) yields of 44.1/20.9 μmol/(g∙h) and an overall photo-activity of 394.6 μmol/(g∙h), 6.5 times higher than that of anatase TiO2 microsphere (AMS) alone. The effects of ZnPy4/MnOx species on the light absorption, photo-induced charge separation, photo-electrochemical behavior, adsorption/activation capacity of reactants (CO2/H2O) and photocatalytic CO2RR performance of the AMS were studied, and it is found that a direct Z-scheme charge transfer mechanism proceeds in the hybrid material via H-bonding formed between the ZnPy4 and Mn/AMS components to boost the photocatalytic CO2RR activity. These results present an effective strategy for fabricating high-performance artificial photosynthesis for solar-driven CO2 conversion via the hybridization of semiconductor with porphyrin derivative.

Insight into the Synergistic Collaboration of g‐C3N4/SnO2 Composites for Photoelectrocatalytic CO2 Reduction

AbstractA novel method for constructing a g‐C3N4/SnO2 heterostructure for CO2 reduction reaction (CO2RR) is presented. In the heterostructure, the introduction of g‐C3N4 makes for restraining the recombination of photo‐induced electrons and holes while the existence of SnO2 plays a vital role in selective catalytic reduction of CO2 into HCOOH, thus their cooperative interaction makes the photoelectric property of g‐C3N4/SnO2 towards CO2RR improved greatly. The so‐fabricated g‐C3N4/SnO2 shows an exclusive HCOOH selectivity and a high faradic efficiency of 58 %, which is about 8 times higher than that of single SnO2. The photocurrent reaches 7.5 μA cm−2 under 0.5 V. Besides, the overpotential is as low as 300 mV (vs. RHE). Moreover, the PL emission decreases obviously after the introduction of g‐C3N4. Given these performance advantages of g‐C3N4/SnO2, the solution‐processed strategy with post‐annealing treatment offers a facile, efficient, yet scalable approach reference to construct CO2RR heterostructure catalysts, which shows higher potential in CO2RR electrocatalysis.

Water coordinated on Cu(I)-based catalysts is the oxygen source in CO2 reduction to CO

Catalytic reduction of CO2 over Cu-based catalysts can produce various carbon-based products such as the critical intermediate CO, yet significant challenges remain in shedding light on the underlying mechanisms. Here, we develop a modified triple-stage quadrupole mass spectrometer to monitor the reduction of CO2 to CO in the gas phase online. Our experimental observations reveal that the coordinated H2O on Cu(I)-based catalysts promotes CO2 adsorption and reduction to CO, and the resulting efficiencies are two orders of magnitude higher than those without H2O. Isotope-labeling studies render compelling evidence that the O atom in produced CO originates from the coordinated H2O on catalysts, rather than CO2 itself. Combining experimental observations and computational calculations with density functional theory, we propose a detailed reaction mechanism of CO2 reduction to CO over Cu(I)-based catalysts with coordinated H2O. This study offers an effective method to reveal the vital roles of H2O in promoting metal catalysts to CO2 reduction.

Deactivation and Stabilization Mechanism of Photothermal CO2 Hydrogenation over Black TiO2

Photothermal catalytic reduction of CO2 is a powerful way to promote carbon neutralization goals. However, there are few reports on the deactivation of the photothermal CO2 reduction reaction. Here, we observed an interesting deactivation phenomenon of photothermal CO2 conversion over TiO2–xHx (black TiO2). Despite the presence of a reducing atmosphere of H2, the oxygen vacancy concentration of TiO2–xHx is reduced, resulting in the deactivation of photothermal CO2 reduction. After Ni is modified onto TiO2–xHx, Ni can activate H2 to form Hs, and the oxygen vacancy concentration of Ni/TiO2–xHx may be maintained, thus solving the deactivation problem in photothermal CO2 hydrogenation.

A compact heat recirculating spiral geometry for thermal integration for Sabatier reaction in microreactor

Sabatier reaction, the catalytic reduction of CO2 to methane, is a reversible and exothermic reaction that produces CO as a by-product. We use two-dimensional computational fluid dynamics (CFD) simulations to analyze the performance of a three-turn spiral microreactor, useful for portable or modular applications. Spiral reactor has inlet at the center followed by three turns that spirals outwards. It allows thermal integration via co-current self-coupling of Sabatier reaction, which enables utilizing the exothermic heat of methanation for preheating of the cold reactants by hot products. Due to compact nature of the geometry, heat released spreads out in the reactor causing an overall moderation of temperature. A favorable cooling effect is achieved in spiral geometry without using external cooling or feed dilution, merely by the property of reactor configuration. For the base case, 71% conversion with 92.6% selectivity to CH4 is attained. Comparison with counter-current operating strategy in U-bend reactor is presented.

Suppressing byproduct formation for high selective CO2 reduction over optimized Ni/TiO2 based catalysts

One of the challenges for catalytic CO2 reduction is to control product selectivity, and new findings that can modify selectivity would be transformative. Herein, two kinds of TiO2 (homemade and commercial) with the same crystal phase but different surface properties are chosen as supports to prepare Ni-based catalysts for CO2 reduction, which show distinctly different product selectivity for CO2 reduction to CH4 or CO, as well as the CO2 conversion. The catalysts based on the homemade TiO2 support are highly selective for CH4 formation, while the latter ones are about 100% selective for CO formation under the same reaction conditions. In addition, the former ones are much active (more than 3 times) than the latter ones. We found that the collaborative contribution of Ti3+ and Ni2+ species and the electronic metal-support interactions effect maybe the main driving force behind for determining the product selectivity. Methane is almost exclusively produced over the catalysts with abundant Ti3+ and Ni2+ species and greater electronic metal-support interaction, otherwise, it will give priority to CO generation. The addition of CeO2 can reduce the Ni particle size and improve the dispersion of Ni nanoparticles, as well as create more Ti3+ species, contributing to the enhancement of CO2 conversion, but shows a negligible effect on product selectivity. Furthermore, the in situ DRIFT experiments and kinetic experiments indicate that the CO route is probably involved in the CO2 reduction process over the homemade Ni-CeO2/TiO2-CO catalyst with abundant Ti3+ and Ni2+ species and a strong electronic transform effect.

Photothermal catalysis for CO2 conversion

The conversion of carbon dioxide into useful fuels or chemical feedstocks is of great importance for achieving carbon emission peak and carbon neutrality. The harvesting and conversion of solar energy will provide a sustainable and environmentally friendly energy source for human production and living. Very recently, photothermal catalysis has been proved to exhibit great advantages in reducing the reaction temperature, promoting the catalytic activity, and manipulating the reaction pathway in comparison with traditional thermal catalysis. In this review, we firstly introduced the fundamental mechanisms and categories of photothermal catalysis to understand the synergy or the difference between photochemical and thermochemical reaction pathways. Subsequently, the criteria and strategies for photothermal catalyst design are discussed in order to inspire the development of high-efficiency photothermal catalytic route by achieving intense absorption of broadband solar energy spectrum and high conversion capability of solar-to-heat. Recent progress in CO2 reduction achieved by photothermal catalysis was summarized in terms of production types. In the end, the future challenges and perspectives of photothermal catalytic CO2 reduction are presented. We hope that this review will not only deepen the understanding of photothermal catalysis, but also inspire the design, preparation and application of high-performance photothermal catalysts, aiming at alleviating non-renewable fossil energy consumption and carbon emissions for early carbon emission peak and carbon neutrality.

Photocatalytic reduction of CO2 and degradation of Bisphenol-S by g-C3N4/Cu2O@Cu S-scheme heterojunction: Study on the photocatalytic performance and mechanism insight

An efficient g-C3N4/Cu2O@Cu plasmonic Step-scheme (S-scheme) heterojunction photocatalyst was successfully designed and used for the degradation of pollutants and energy generation. The removal of Bisphenol-S pollutants and catalytic reduction of CO2 for hydrocarbon fuel production experiments under the visible light irradiation showed that the catalyst displayed good stability and perfect photocatalytic performance. Among the prepared samples, g-C3N4/Cu2O@Cu-4 displayed the highest catalytic performance, which was attributed to the high light absorption capacity and the efficient interfacial charge separation in the S-scheme heterojunction. From the viewpoint of practical wastewater treatment, a series of the effects of environmental factors, such as initial pollutant concentration, inorganic salts, organic compounds and various water sources on the photocatalytic performance were investigated. Eight intermediate products formed in the photocatalytic oxidation of Bisphenol-S were confirmed by the GC-MS, and the proposed photocatalytic degradation pathway of Bisphenol-S was suggested according to the intermediate products. Importantly, the charge density difference of the interface between g-C3N4 and Cu2O (g-C3N4/Cu2O) as well as the interface between Cu and Cu2O (Cu/Cu2O heterostructures) was calculated, respectively. The calculated results verified that the built-in electric field had been established at their interface. Spatial separation of photogenerated electron-hole pairs in the S-scheme g-C3N4/Cu2O@Cu heterojunction was realized through the built-in electric field.