Enhanced CO2 Reduction Research Articles

Enhanced CO2 reduction with hydrophobic cationic-ionomer layer-modified zero-gap MEA in acidic electrolyte.

A hydrophobic cationic-ionomer layer of quaternary ammonium poly(N-methyl-piperidine-co-p-terphenyl) and PTFE is presented to enhance the CO2 electroreduction in a zero-gap membrane electrode assembly (MEA) electrolyzer under acidic and low alkali ion concentration conditions. The modified MEA achieved a maximum CO faradaic efficiency of 95.6% at 100 mA cm-2.

Enhancing photocatalytic CO2 reduction via a single-domain ferroelectric Z-scheme heterojunction of BiFeO3/CsPbBr3 inducing dual built-in electric fields

A Z-scheme heterojunction designed via hot injection method enables growth of nanocrystals on nanosheets. This single-domain design causes a polarization electric field within the nanosheets and an electric field at the heterojunction interface. Both drive charge separation enhancing CO2 reduction.

Recent developments in piezo-photocatalytic CO2 reduction: concepts, mechanism, and advances.

Out of the high number of photocatalytic applications, CO2 reduction has proved to be quite a boon for the present world. Increasing CO2 emissions owing to fossil fuel usage has been a menace to our society. To date, many methods have been developed to redress the situation. One of them is photocatalysis, which has been a well-known branch of energy and environmental applications since 1972. This is due to its low energy consumption and green nature. In recent years, a new phenomenon has come into existence wherein a combination of mechanical energy and photocatalysis can increase the efficiency of any catalytic process. In this regard, this frontier article will discuss the recent developments in piezo-photocatalysis for CO2 reduction. The main focus will be understanding the underlying mechanisms of efficiency enhancements in photocatalytic systems. Initially, the mechanism of CO2 reduction and its current needs will be discussed in the introduction. Further, a collection of recent reports from the literature and various material systems will be discussed to gain insights into the latest developments in the area. Then, literature and references that are purely mechanism-based with deeper analysis will be discussed, along with crucial characterization techniques for piezo-photocatalysts. Many factors need to be factored in for a better understanding of piezo-photocatalysis, e.g., factors such as piezo energy source, material design, and CO2 adsorption, require more attention to increase the CO2 reduction capability of photocatalysts. Based on the discussions in this article, researchers will gain new perceptions on the combination of vibrational energy and light energy to enhance CO2 reduction yields. Moreover, this article can advance understanding of techniques such as Kelvin probe microscopy, the requirement of simulation studies, and CO2 reduction mechanisms to better understand the piezo behavior of materials and ways to improve them for maximum product yield.

Artificial CO2 photoreduction: a review of photocatalyst design and product selectivity regulation

We summarized the design strategies for photocatalysts to enhance CO2 reduction and accepted pathways for selective photocatalytic CO2 conversion.

Amino-functionalization enhanced CO2 reduction reaction in pure water.

The electrochemical reduction of carbon dioxide (CO2RR) to carbon monoxide represents a cost-effective pathway towards realizing carbon neutrality. To suppress the hydrogen evolution reaction (HER), the presence of alkali cations is critical, which can however lead to precipitate formation on the electrode, adversely impacting the device stability. Employing pure water as the electrolyte in zero-gap CO2 electrolyzers can address this challenge, albeit at the cost of diminished catalyst performance due to the absence of alkali cations. In this study, we introduce a novel approach by implementing amino modifications on the catalyst surface to mimic the function of alkali metal cations, while simultaneously working in pure water. This modification enhances the adsorption of carbon dioxide and protons, thereby facilitating the CO2RR while concurrently suppressing the HER. Utilizing this strategy in a zero-gap CO2 electrolyzer with pure water as the anolyte resulted in an impressive carbon monoxide faradaic efficiency (FECO) of 95.5% at a current density of 250 mA cm-2, while maintaining stability for over 180 hours without any maintenance.

Efficient photoreduction of carbon dioxide to acetaldehyde on monatomic defective black phosphorus

Conversion of CO2 into C2 products has been challenging, largely due to the insufficient electron deliverability of catalyst. Here we proposed latent monatomic defective black phosphorus (BPV), on which the efficient photoreduction of CO2 to CH3CHO was confirmed by density functional theory (DFT) calculations. The electrostatic potential difference between the upper and lower atoms of the BPV was found responsible for the enhanced separation of electrons and holes. The COCO coupling was studied, the charge transfer from BPV to CO (0.38 |e|) was found contributes to the enhanced CO2 reduction reaction (CO2RR) activity and promoted COCO coupling process. This work provides theoretical guidelines on the design of defect catalyst for CO2 photoreduction.

Azobenzene-equipped Covalent triazine polymers for Visible-Light-Driven photocatalytic reduction of CO2 to CH4

Covalent triazine polymers, as large π conjugated, highly porous, nitrogen riched organic semiconductors, can play a key role in tackling the fuel energy crisis and global warming issues. However, their development in photocatalytic CO2 reduction is still rare. More effective strategies to enhance CO2 reduction activity need to be explored. Herein, different amounts of azobenzene pendants functionalized CTPs: Azo-CTP0, Azo-CTP1, Azo-mCTP1 and Azo-CTP2, were fabricated for photocatalytic CO2 reduction with Pd loaded. Among them, Azo-mCTP1 displayed the highest CO2 uptake capacity up to 48.2 cm3 g−1 (2.15 mmol g−1) at 273 K, and the highest CH4 evolution rate in the water system, with selectivity highly up to 97 %. Apart from that, the azobenzene functionalization of Azo-CTP0 could significantly boost the CO2 reduction efficiency by 4 times. Therefore, this study provides a potentially general approach for accurately modifying organic semiconductors to enhance photocatalytic performance.

Thermo-chemical disposal of plastic waste from end-of-life vehicles (ELVs) using CO2

The source reduction of plastic waste could be an effective means to attenuate hazardous environmental problems triggered by microplastics. Energy recovery from plastic waste through thermochemical processes is a desirable valorization route. To realize the grand challenges, plastic waste derived from end-of-life vehicles (ELVs) was pyrolyzed. To propose a greener feature, CO2 was introduced as a mediator to maximize carbon allocation to the gaseous pyrogenic product (syngas) by CO2 reduction to CO and concurrent oxidation of volatile matter (VM) that was evolved from the thermolysis of plastic waste. As such, fundamental and systematic works were conducted to delineate the CO2 effects on conversion of VMs. This study experimentally proved that CO2 promotes thermal cracking in line with C–C bond scissions. However, the reaction rate for the conversion of CO2 and VM into CO via homogeneous reaction was not fast. Therefore, a Ni-based catalyst was employed to accelerate the reaction rate. However, there was coke deposition on the catalyst surface. To prevent coke formation, we chose a method to enhance CO2 reduction to CO and the oxidation of VM. Thus, three bimetallic catalysts were used for catalytic pyrolysis. Among the three bimetallic catalysts, Rh0.1Ni1/SiO2 was the most effective.

Exploring the synergistic effects of chemical activation and N-doping in carbon nanospheres for advanced Li–CO2Mars batteries

Lithium-CO2 batteries can be used to mitigate CO2 emissions by recycling CO2 for energy storage and potential utilization as a standalone energy storage device on Mars as it contains 95 % CO2 (Li–CO2Mars batteries). The incomplete decomposition of the discharge product, Li2CO3, reduces the battery's cycle life, limiting its practicability. Herein, we develop a hierarchical porous, high surface area (1845 m2 g−1) activated N-doped candle soot (ANCS) carbon catalyst by modifying the candle soot carbon through the combination of the techniques of activation and hereroatom N-doping for enhanced CO2 reduction and evolution reactions. The ANCS-based Li–CO2Mars batteries exhibit a high discharge capacity of 11,490 mAh g−1 and a stable cycle life of over 130 cycles with a low overpotential of 1.4 V at the high current density of 200 mA g−1. Furthermore, density functional theory (DFT) studies reveal that the ANCS catalyst's higher affinity for CO2 adsorption and Li2CO3 production leads to the excellent performance of the Li–CO2Mars batteries. The developed method offers way of repurposing the pollutant carbons as metal-free carbon catalysts for the future progress of the Li–CO2Mars batteries for use as a future sustainable energy source for both Earth and Mars.

Improving Cycle Stability and Kinetics of Rechargeable Al/CO2 Batteries By Functional Cathode Materials

Metal-CO2 batteries have emerged as a promising solution for advancing energy storage technology and sequestering carbon dioxide from ambient air. Aluminum (Al) is an appealing anode material for electrochemical CO2 capture and conversion due to its lower cost and reactivity in comparison to lithium and sodium anode materials, making it safer and more accessible for manufacturing. Its abundance across various regions of the world further adds to Al’s attractiveness. Additionally, Aluminum boasts a high specific energy of 2980A·hour/kg, suggesting that its electrochemical conversion with CO2 can produce large amounts of electrical energy. Previous study shows that Aluminum/CO2 batteries possess a remarkable discharge capability with the introduction of a small amount of oxygen, however, these batteries are not rechargeable.By utilizing a homogeneous iodine-based redox mediator, our group demonstrated that the Al-CO2 battery can achieve reversible discharge and charge with minimal overpotential of 0.05V, reducing stripping/plating overpotentials by 40% across various current rates compared to an unmodified imidazolium-based ionic liquid electrolyte. This is achieved by replacing oxygen gas with aluminum iodide in the electrolyte, which maintains high discharge capacity and enables the battery to be recharged for up to 12 cycles at a 20 mA/gcarbon rate.Examining the discharge and charge rates of different cathode materials was necessary to demonstrate the improvement in cycle stability. By utilizing functional carbon-based materials with increased surface area, heteroatom doping and unique pore structure as the cathode, we demonstrate that the rechargeable Al-CO2 battery can enhance CO2 reduction during the discharge processes, thereby improving reaction kinetics.Higher surface area and porous materials facilitate faster electron transfer during the electrochemical reactions while allowing better CO2 diffusion into the cathode, improving reaction rates.

Synergistic adsorption and kinetic studies of heterostructured g-C3N4/TiO2 nano-photocatalyst under visible light for enhanced CO2 reduction.

Graphitic carbon nitride (g-C3N4) and titanium dioxide (TiO2) were synthesized using sol-gel and ultrasonic impregnation technique followed by calcination for photocatalytic CO2 reduction. The nano-photocatalysts were analyzed for their morphological, structural, and optical characteristics. Scanning electron microscopy (SEM) revealed the presence of spherical and layered sheet-like nanoparticles, as well as the occurrence of minor aggregations. The ultraviolet-visible spectroscopy (UV-vis) revealed that g-C3N4 has good photocatalytic properties with a medium band gap (2.7eV), and TiO2 has high charge transfer potentials, robust oxidation properties, and high band gap (3.20eV). However, the larger band gap makes it unresponsive in the visible light spectrum. In order to circumvent this constraint, a hybrid heterostructured g-C3N4/TiO2 catalyst with different compositions, viz., 1:1, 1:2, and 2:1, were fabricated using the ultrasonic impregnation technique followed by calcination process. The optical band gap of g-C3N4/TiO2 nanocomposite shows a red shift towards 2.85eV from 3.20eV for bare TiO2, inferring enhanced absorption in the visible light region. Further, the photocatalytic experiments were performed using visible light sources for all the catalysts. The g-C3N4/TiO2 (2:1) reported higher photocatalytic activity due to its reduced crystallite size of 12.94nm which were investigated using X-ray diffraction analysis (XRD) and lower band gap of 2.85eV. The study infers that hybrid photocatalyst enhances the visible light absorption, electron-hole (e - /h +) pair separation rate, and photocatalytic reduction of CO2. In addition, two adsorption models Langmuir and Freundlich were used and adsorption kinetic data were fitted to pseudo-first-orderreaction for all thefive catalysts. The adsorption isotherm of CO2 by g-C3N4/TiO2 (2:1) wellfitted by the Freundlich adsorption equation. On the basis of adsorption magnitude (n) values (1.74), it was found that the interaction between CO2 molecules and g-C3N4/TiO2 occurs according to the chemisorption mechanism. The kinetic study infers that the highest value of apparent rate constant (kapp) was exhibited by g-C3N4/TiO2 (2:1), which indicates that the products predominate at equilibrium.

In-CdS@ZIF-8&FDH photo-enzyme nanosystem with high NADH regeneration ability via indium doping for enhanced CO2 reduction to formic acid

Replacement of fossil fuel by renewable resources is a central resource and energy efficiency strategy, where CO2 is the key molecule to proceed effectively in this direction. Here, we synthesized In-doped CdS and constructed a new photo-enzyme nanosystem 10 %In-CdS@ZIF-8&FDH, which can catalyze CO2 to formic acid (HCOOH) via formate dehydrogenase immobilized on ZIF-8 while photocatalytic regenerating NADH via indium-doped CdS. Indium doping greatly enhances the photocatalytic performance of CdS. The NADH regeneration rate reaches 94.10 %. The nanosystem can produce 267.18 μM HCOOH, which is 4.27 times that of the free enzyme system. And 85.98 % of the residual activity can be retained after reusing 8 times. This study will inspire more research efforts for light-driven enzymatic nanosystems in CO2 fixation and lay the foundation for realizing renewable energy-driven CO2 conversion to produce chemical products.

Microwave resonance enhanced CO2 reduction using biochar

Microwave resonance enhanced CO2 reduction using biochar

Minimizing CO2 emissions by photocatalytic CO2 reduction to CH3OH over Li2MnO3/WO3 heterostructures under visible illumination

Photocatalytic CO2 reduction to valuable fuels has proved to be a favourable process to produce renewable energy and reduce CO2 emissions, which mostly depends on designing effective photocatalysts with the rapid separation rate of charge carriers. In this contribution, mesoporous n-n heterojunction Li2MnO3/WO3 nanocomposites were designed via a simplistic sol-gel process for CO2 reduction utilizing visible illumination (λ > 420 nm). XRD and TEM measurements confirmed the synthesized Li2MnO3/WO3 nanocomposite is a monoclinic structure, and its particle size is 25 ± 5 nm. The obtained Li2MnO3/WO3 exhibited narrower bandgap energy (1.74 eV), larger surface area (212 m2g−1), exceedingly visible absorbing, and lower recombination of electron and hole. The yield of CH3OH was determined about 198, 871, 1140, 1550 and 1570 mmolg−1 for bare WO3 and 5%, 10%, 15% and 20% Li2MnO3/WO3 nanocomposites, respectively. These results evidenced that the 15% Li2MnO3/WO3 photocatalyst exhibited the best reduction ability compared to other nanocomposites. The CO2 reduction over 15% Li2MnO3/WO3 photocatalyst achieved a maximal CO2 conversion with the substantially boosted CH3OH, i.e., 1550 mmolg−1 after 9 h, which was enhanced 7.8 folds great than of WO3 NPs. Mesoporous Li2MnO3/WO3 nanocomposites, in comparison with bare WO3 NPs, created more active sites for facilitating CO2 and had a specific electric field to more effectively separate charge carriers. The Li2MnO3/WO3 photocatalyst has superior photostability during the continuous reduction of CO2 for 45 h with no remarkable decrease. The possible direct S-scheme mechanism for electron transfer over Li2MnO3/WO3 photocatalyst with the enhanced CO2 reduction ability was discussed. The present work demonstrates an avenue for building highly effective heterostructure photocatalysts in solar-energy-induced potential applications.

Creation of robust oxygen vacancies in 2D ultrathin BiOBr nanosheets by irradiation through photocatalytic memory effect for enhanced CO2 reduction

An interesting photocatalytic memory effect was found in 2D ultrathin BiOBr nanosheets, which endowed them the capability to trap photogenerated electrons on Bi3+ and Br- in this material system for an extended period of time and resulted in the creation of stable oxygen vacancies (Ov) by just visible light irradiation due to the charge balance requirement. Thus, a broader visible light absorption, more negative conduction band minimum, stronger piezoelectric response, better charge carrier separation and transfer, and enhanced CO2 adsorption and activation were occurred in these BiOBr nanosheets with prior visible light irradiation, all of which were beneficial for their enhanced CO2 reduction performances in photocatalysis, piezocatalysis, and photopiezocatalysis, respectively, than their counterparts without it. This work demonstrated a novel approach to create oxygen vacancies by light irradiation through the photocatalytic memory effect, which could be readily applied to similar photocatalyst systems to boost their performances and generate novel functionalities.

Synergizing interstitial K and substitutional O by dual-doping on carbon nitride for efficient CO2 photoreduction

Photocatalytic CO2 reduction is a promising tactic to fix surplus CO2 and generate high-value products. Non-metallic graphitic carbon nitride (CN) is a robust and inexpensive photocatalyst for CO2 reduction, yet its efficiency remains limited by poor light absorption, sluggish charge kinetics, and low surface area. Here, we report K and O dual-doped CN (K/O-CN) synthesized by facile molten salt calcination for efficient CO2 photoreduction. Distinctive from CN, K/O-CN owned regular nanorod structure and introduced cyano terminal groups, due to the reconstruction of C-N bond by interstitial K doping and substitutional doping of O within CN matrix. K/O-CN displayed a CO production rate of 4.5 ± 0.2 μmol g−1h−1, which was 7.5 times as much as pristine CN and surpassed the performance of O-CN or K-CN. The enhanced CO2 reduction of K/O-CN was derived from its enlarged surface area and pore volume, magnified CO2 adsorption capacity, and narrowed band gap with better visible light absorption. The dual-doping of K and O accelerated the charge separation and reinforced reduction potential with a more negative conduction band. DFT calculation reveals that dual-doping impeded charge recombination by increasing spatial distance between photoinduced electrons and holes and caused a kinetic preference for CO desorption.

Unraveling the impact of Cu-doping in lead free halide perovskites for markedly enhancing photocatalytic CO2 reduction performance

Excessive CO2 emissions from the consumption of fossil fuels contribute to both global warming and the energy crisis. To address these pressing issues, it is essential to capture and convert CO2 into chemical feedstock using renewable energy such as solar energy. Solar-powered photocatalytic fuel production is widely acknowledged as a viable solution for a sustainable energy future. However, the development of high-performance photocatalysts remains a significant challenge to overcome in this endeavor. Recently, lead-free perovskites have emerged as a promising category of materials for CO2 photoreduction, thanks to their remarkable optoelectronic properties, cost-effective solution processing, and non-toxic nature. Nonetheless, their inherent photocatalytic CO2 reduction activity remains low due to the insufficient separation of photogenerated charges and the lack of active sites. Here, we demonstrate that Cu doping in lead-free double perovskites can lead to markedly enhanced CO2 reduction performance. The interstitial Cu dopants modulate the fermi level and introduce the active energy sites near the conduction band, which significantly enhances light absorption and separation of charge carriers. The Cu-Cs2AgBiCl6 shows the activity of 88 and 48 µmol/gcat for CH4 and CO products which are both higher than those of the pristine Cs2AgBiCl6 (27 and 10 µmol/gcat). The total yield of Cu-Cs2AgBiCl6 perovskite for CO2 photoreduction is superior to those reported under similar conditions. Transient absorption results show that hot carrier relaxation is slower and carrier decay lifetime is extended in Cu-Cs2AgBiCl6, which can enhance the charge migration efficiency and boost the CO2 reduction performance. These findings provide valuable insight into the mechanism of CO2 reduction in Cu-doped Cs2AgBiCl6 perovskite crystals and suggest that Cu-doping is a promising strategy for developing highly efficient and selective CO2 reduction photocatalysts.

Investigating the synergistic effect of sulfur and nitrogen co-doping in graphene for enhanced CO2 reduction to CO: A computational study

Recently, N and S co-doped graphene showed excellent activity and selectivity for electrochemical CO2 reduction (CO2RR) to CO, much better than that of singly N doped counterpart, but the underlying mechanism of S promotional effect is still elusive. Here, by using density functional theory (DFT) calculation, N or S singly doped graphene and co-doped graphene for CO2RR to CO and competitive hydrogen evolution reaction (HER) are compared to reveal the synergy effect. The results show that singly S doped graphene exhibits negligible activity for CO production because of high formation energy of COOH intermediate, whereas graphene doped with pyridinic N and pyrrolic N show moderate energy barrier for CO2RR, but N atom would be easily passivated due to strong binding with H atom. In N and S co-doped graphene, N and S pair prefer to replace CC bond, but they are not bonded. In this configuration, the S atom can serve as active site, having even lower energy barrier for CO2RR than that of pyridinic N, meanwhile the S atom is not passivated by hydrogen atom. The electronic origin of enhanced activity for S atom is also presented.

Selectivity control of photocatalytic CO2 reduction over ZnS-based nanocrystals: A comparison study on the role of ionic cocatalysts

Taking copper doped ZnS (ZnS:Cu) nanocrystals as the main body of photocatalyst, the influence of different base transition metal ions (M2+ = Ni2+, Co2+, Fe2+ and Cd2+) on photocatalytic CO2 reduction in inorganic reaction system is investigated. Confined single-atom Ni2+, Co2+, and Cd2+ sites were created via cation-exchange process and enhanced CO2 reduction, while Fe2+ suppressed the photocatalytic activity for both water and CO2 reduction. The modified ZnS:Cu photocatalysts (M/ZnS:Cu) demonstrated tunable product selectivity, with Ni2+ and Co2+ showing high selectivity for syngas production and Cd2+ displaying remarkable formate selectivity. DFT calculations indicated favorable H adsorption free energy on Ni2+ and Co2+ sites, promoting the hydrogen evolution reaction. The selectivity of CO2 reduction products was found to be sensitive to the initial intermediate adsorption states. *COOH formed on Ni2+ and Co2+ while *OCHO formed on Cd2+, favoring the production of CO and HCOOH as the main products, respectively. This work provides valuable insights for developing efficient solar-to-fuel platforms with controlled CO2 reduction selectivity.

Achieving Efficient CO2 Electrolysis to CO by Local Coordination Manipulation of Nickel Single-Atom Catalysts.

Selective electroreduction of CO2 to C1 feed gas provides an attractive avenue to store intermittent renewable energy. However, most of the CO2-to-CO catalysts are designed from the perspective of structural reconstruction, and it is challenging to precisely design a meaningful confining microenvironment for active sites on the support. Herein, we report a local sulfur doping method to precisely tune the electronic structure of an isolated asymmetric nickel-nitrogen-sulfur motif (Ni1-NSC). Our Ni1-NSC catalyst presents >99% faradaic efficiency for CO2-to-CO under a high current density of -320 mA cm-2. In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy and differential electrochemical mass spectrometry indicated that the asymmetric sites show a significantly weaker binding strength of *CO and a lower kinetic overpotential for CO2-to-CO. Further theoretical analysis revealed that the enhanced CO2 reduction reaction performance of Ni1-NSC was mainly due to the effectively decreased intermediate activation energy.