CO2 Reduction In Aqueous Solution Research Articles

Organic Polymer Dots Photocatalyze CO2 Reduction in Aqueous Solution

AbstractDeveloping low‐cost and efficient photocatalysts to convert CO2 into valuable fuels is desirable to realize a carbon‐neutral society. In this work, we report that polymer dots (Pdots) of poly[(9,9′‐dioctylfluorenyl‐2,7‐diyl)‐co‐(1,4‐benzo‐thiadiazole)] (PFBT), without adding any extra co‐catalyst, can photocatalyze reduction of CO2 into CO in aqueous solution, rendering a CO production rate of 57 μmol g−1 h−1 with a detectable selectivity of up to 100 %. After 5 cycles of CO2 re‐purging experiments, no distinct decline in CO amount and reaction rate was observed, indicating the promising photocatalytic stability of PFBT Pdots in the photocatalytic CO2 reduction reaction. A mechanistic study reveals that photoexcited PFBT Pdots are reduced by sacrificial donor first, then the reduced PFBT Pdots can bind CO2 and reduce it into CO via their intrinsic active sites. This work highlights the application of organic Pdots for CO2 reduction in aqueous solution, which therefore provides a strategy to develop highly efficient and environmentally friendly nanoparticulate photocatalysts for CO2 reduction.

A Polymeric Unimolecular CO Dehydrogenase Mimic with both Inner and Outer Spheres for Enhanced Photocatalytic CO2 Reduction in Aqueous Solution.

Inspired by carbon monoxide dehydrogenase (CODH), mimicking its inner and outer spheres is a promising strategy in CO2 reduction catalyst design. However, artificialCODH-like catalysts are generally limited to the inner sphere effect and only applicable in organic solvents or for electrocatalysis. Herein, we report an aqueous CODH mimic with both inner and outer spheres for photocatalysis. In this polymeric unimolecular catalyst, the inner sphere is composed of cobalt porphyrin with four appended amido groups and the outer sphere consists of four poly(2(dimethylamino)ethyl methacrylate) (PDMAEMA) arms. Upon visible light irradiation (λ > 420 nm), the as-prepared photocatalyst exhibits a high turnover number (TONCO = 1731.2) in the reduction of CO2 into CO, which is superior to most reported molecular photocatalysts in aqueous solution. The mechanism studies indicate that, in this water-dispersible and structurally well-defined CODH mimic, the cobalt porphyrin core serves as the catalysis center, amido groups function as hydrogen-bonding pillars helping to stabilize the CO2 adduct intermediate, while PDMAEMA shell renders both the water solubility and a CO2 reservoir through reversibly capturing of CO2. The present work has clarified the significance of inner and outer coordination sphere effects for improving the aqueous photocatalytic CO2 reduction performance of CODH mimics.

Gallium Oxide Assisting Ag-Loaded Calcium Titanate Photocatalyst for Carbon Dioxide Reduction with Water

An efficient and highly selective photocatalytic conversion of carbon dioxide (CO2) into valuable chemicals such as carbon monoxide (CO) using water (H2O) as an electron donor has been much attractive and deeply desired, which requires the development of advanced photocatalysts based on a functional design. As the Ag-loaded calcium titanate (CaTiO3, CTO) photocatalyst showed a high selectivity to CO2 reduction in aqueous solution and the Ag-loaded gallium oxide (Ga2O3) photocatalyst showed a higher activity for both H2O splitting and CO2 reduction, herein, a series of composite photocatalyst samples consisting of Ga2O3 and CTO were simply fabricated by calcination of the physical mixtures, followed by loading of a Ag cocatalyst with a photodeposition method. The optimized sample with the Ag cocatalyst exhibited both a high CO formation rate of 56.9 μmol h–1 (higher than that of Ag/Ga2O3) and a high selectivity of 95.0% (comparable to Ag/CTO) in the photocatalytic CO2 reduction with H2O. In this composite photocatalyst, most of the electrons generated in the photoexcited Ga2O3 part migrated to the minor CTO particles to contribute to the selective CO2 reduction reaction, which was evidenced by the selective photodeposition of Ag species on the CTO part. The selective CO formation originates from the property of Ag-loaded CTO photocatalyst as the active part in the composite photocatalyst. The Ga2O3 part functions as an antenna to receive the light and donate the photoexcited electrons to the much decorated Ag/CTO part, where the concentrated electrons would promote CO2 reduction with high efficiency.

Recent progress in C–N coupling for electrochemical CO2 reduction with inorganic nitrogenous species in aqueous solution

The electrocatalytic CO2 reduction in aqueous solution mainly involves bond cleavage and formation between C, H and O, and it is highly desirable to expand the bond formation reaction of C with other atoms to obtain novel and valuable chemicals. The electrochemical synthesis of N-containing organic chemicals in electrocatalytic CO2 reduction via introducing N sources is an effective strategy to expand the product scope, since chemicals containing C–N bonds (e.g. amides and amines) are important reactants/products for medicine, agriculture and industry. This article focuses on the research progress of C–N coupling from CO2 and inorganic nitrogenous species in aqueous solution. Firstly, the reaction pathways related to the reaction intermediates for urea, formamide, acetamide, methylamine and ethylamine are highlighted. Then, the electrocatalytic performance of different catalysts for these several N-containing products are summarized and classified. Finally, the challenges and opportunities are analyzed, aiming to provide general insights into future research directions for electrocatalytic C–N coupling.

Direct observation of bicarbonate and water reduction on gold: understanding the potential dependent proton source during hydrogen evolution.

The electrochemical conversion of CO2 represents a promising way to simultaneously reduce CO2 emissions and store chemical energy. However, the competition between CO2 reduction (CO2R) and the H2 evolution reaction (HER) hinders the efficient conversion of CO2 in aqueous solution. In water, CO2 is in dynamic equilibrium with H2CO3, HCO3 -, and CO3 2-. While CO2 and its associated carbonate species represent carbon sources for CO2R, recent studies by Koper and co-workers indicate that H2CO3 and HCO3 - also act as proton sources during HER (J. Am. Chem. Soc. 2020, 142, 4154-4161, ACS Catal. 2021, 11, 4936-4945, J. Catal. 2022, 405, 346-354), which can favorably compete with water at certain potentials. However, accurately distinguishing between competing reaction mechanisms as a function of potential requires direct observation of the non-equilibrium product distribution present at the electrode/electrolyte interface. In this study, we employ vibrational sum frequency generation (VSFG) spectroscopy to directly probe the interfacial species produced during competing HER/CO2R on Au electrodes. The vibrational spectra at the Ar-purged Na2SO4 solution/Au interface, where only HER occurs, show a strong peak around 3650 cm-1, which appears at the HER onset potential and is assigned to OH-. Notably, this species is absent for the CO2-purged Na2SO4 solution/gold interface; instead, a peak around 3400 cm-1 appears at catalytic potential, which is assigned to CO3 2- in the electrochemical double layer. These spectral reporters allow us to differentiate between HER mechanisms based on water reduction (OH- product) and HCO3 - reduction (CO3 2- product). Monitoring the relative intensities of these features as a function of potential in NaHCO3 electrolyte reveals that the proton donor switches from HCO3 - at low overpotential to H2O at higher overpotential. This work represents the first direct detection of OH- on a metal electrode produced during HER and provides important insights into the surface reactions that mediate selectivity between HER and CO2R in aqueous solution.

A water-stable organolead iodide material for overall photocatalytic CO2 reduction

The utilization of perovskites as photocatalysts to convert CO2 into fuels and chemicals has received wide attention recently. However, their instability in water hinders their long-term application for overall photocatalytic CO2 reduction. Herein, we integrate the water-stable perovskite-like organolead iodide crystalline material [Pb8I8(H2O)3]8+[−O2C(CH2)4CO2−]4 (TJU-16) with Au co-catalyst for photocatalytic CO2 reduction in aqueous solution without sacrificial reagent. Under the AM 1.5 G simulated illumination, the TJU-16 with 0.19 wt.‰ Au co-catalyst steadily generated electrons for CO2 reduction reaction, which was 2.2 times of pure TJU-16. The Au0.19/TJU-16 catalyzed CO2 reduction at a rate of 84.2 µmol·g−1·h−1, and achieved a solar-to-fuel (STF) conversion efficiency of 0.034%. Our work will motivate the rational design of water-stable perovskite-like materials for photocatalytic applications.

Coordination-driven discrete metallo-supramolecular assembly for rapid and selective photochemical CO2 reduction in aqueous solution.

A discrete metallo-supramolecular assembly composed of six iron(ii) cations and twelve redox-active terpyridine fragments has been developed for the highly efficient visible-light-driven reduction of CO2 to CO with a TON of 14 956 and 99.6% selectivity in the presence of an organic thermally activated delayed fluorescence (TADF) photosensitizer 4CzIPN in aqueous solution. The photochemical system proceeds rapidly with a turnover frequency (TOF) of 276 min-1. It is demonstrated that the redox-active terpyridine fragments in the assembly are reduced by the photosensitizer which could further act as an electron reservoir for CO2 reduction, resulting in the highly efficient reduction of CO2. This work shows that discrete metallo-supramolecular assemblies could be used for robust photochemical CO2 reduction.

Influence of the Chemical Compositions of Bismuth Oxyiodides on the Electroreduction of Carbon Dioxide to Formate.

Bismuth oxyiodides with varying chemical compositions were fabricated to effectively electrochemical reduce CO2 to formate. Bi5 O7 I and Bi7 O9 I3 nanosheets assemble irregularly, and BiOI nanosheets form a sphere-like structure. Compared with BiOI and Bi7 O9 I3 , Bi5 O7 I exhibits an excellent Faradaic efficiency of 89 % for formate production with the partial current density of 13.2 mA/cm2 at -0.89 V vs. RHE owing to the elevated amounts of Bi metal sites reduced from Bi3+ during electrolysis. The partial current densities of formate on BiOI were higher than those on Bi7 O9 I3 which is attributed to the higher iodine content. The synergistic effect of bismuth and iodine of bismuth oxyiodides is responsible for their electrocatalytic properties during CO2 reduction in aqueous solutions.

Electrochemical reduction of carbon dioxide to formate via nano-prism assembled CuO microspheres

Electrochemical reduction of CO2 has been demonstrated as one of the promising technologies to reduce the greenhouse effect. In this study, nano-prism assembled hierarchical CuO microspheres (Prism-CuO) were designed and used for CO2 electroreduction. The Prism-CuO coated gas diffusion electrode showed high activity for CO2-to-formate conversion with overpotential as low as ∼200 mV, and achieved maximum faradaic efficiency of 65.1% at −1.6 V vs. Ag/AgCl. Moreover, it maintained the stable performance for continuous 20 h of electrolysis. The better performance was mainly attributed to the unique prism feature as it provided abundant corner- and edge-based low-coordinated active reaction sites. These sites could further arouse strong local-electric field to lower the barrier of CO2 adsorption and motivate CO2 activation by accelerating charges transfer process. The result implied designing the nano-prism constructed hierarchical framework would be an efficient strategy to develop the advanced electrocatalyst for efficient CO2 reduction in aqueous solution.

Pyrene-functionalized polymeric carbon nitride with promoted aqueous–organic biphasic photocatalytic CO2 reduction

Covalently grafting pyrene groups on polymeric carbon nitride enables photocatalytic CO2 reduction in aqueous solution with simultaneous alkene oxidation in organic phase.

Tuning Cu/Cu2O Interfaces for the Reduction of Carbon Dioxide to Methanol in Aqueous Solutions

AbstractArtificial photosynthesis can be used to store solar energy and reduce CO2 into fuels to potentially alleviate global warming and the energy crisis. Compared to the generation of gaseous products, it remains a great challenge to tune the product distribution of artificial photosynthesis to liquid fuels, such as CH3OH, which are suitable for storage and transport. Herein, we describe the introduction of metallic Cu nanoparticles (NPs) on Cu2O films to change the product distribution from gaseous products on bare Cu2O to predominantly CH3OH by CO2 reduction in aqueous solutions. The specifically designed Cu/Cu2O interfaces balance the binding strengths of H* and CO* intermediates, which play critical roles in CH3OH production. With a TiO2 model photoanode to construct a photoelectrochemical cell, a Cu/Cu2O dark cathode exhibited a Faradaic efficiency of up to 53.6 % for CH3OH production. This work demonstrates the feasibility and mechanism of interface engineering to enhance the CH3OH production from CO2 reduction in aqueous electrolytes.

Tuning Cu/Cu2 O Interfaces for the Reduction of Carbon Dioxide to Methanol in Aqueous Solutions.

Artificial photosynthesis can be used to store solar energy and reduce CO2 into fuels to potentially alleviate global warming and the energy crisis. Compared to the generation of gaseous products, it remains a great challenge to tune the product distribution of artificial photosynthesis to liquid fuels, such as CH3 OH, which are suitable for storage and transport. Herein, we describe the introduction of metallic Cu nanoparticles (NPs) on Cu2 O films to change the product distribution from gaseous products on bare Cu2 O to predominantly CH3 OH by CO2 reduction in aqueous solutions. The specifically designed Cu/Cu2 O interfaces balance the binding strengths of H* and CO* intermediates, which play critical roles in CH3 OH production. With a TiO2 model photoanode to construct a photoelectrochemical cell, a Cu/Cu2 O dark cathode exhibited a Faradaic efficiency of up to 53.6 % for CH3 OH production. This work demonstrates the feasibility and mechanism of interface engineering to enhance the CH3 OH production from CO2 reduction in aqueous electrolytes.

Water-Soluble Manganese Complex for Selective Electrocatalytic CO2 Reduction to CO

Relatively few solution electrocatalysts for CO2 reduction in aqueous solutions are reported. However, to be sustainable, electrocatalytic CO2 reduction is likely to be coupled to water oxidation in a complete device. Here we report a water-soluble Mn polypyridyl complex for the electrocatalytic reduction of CO2 to CO. This complex shows activity across a broad pH range and an excellent selectivity at pH 9 (3.8:1, CO/H2). Cyclic voltammetry indicates activity across a range of different electrode materials (boron-doped diamond, glassy carbon, and Hg/Au amalgams).

Metallic nanocatalysts for electrochemical CO2 reduction in aqueous solutions

How to effectively and efficiently reduce carbon dioxide (CO2) to value-added chemicals represent a frontier in catalysis research. Due to the high activation energy needs and the endothermic nature of CO2 reduction, the reactions are difficult to carry out. When H2O is present, hydrogen evolution reactions (HER) often compete favorably with CO2 reduction reactions. For these reactions, catalysts are of critical importance to CO2 reduction. In this article, we review the various metal nanocatalysts for electrochemical CO2 reduction (ECR) reactions. In recognition of the importance of H2O to CO2 reduction, we focus our discussions on systems in aqueous solutions. Nanostructured metal catalysts are chosen for the discussions because they represent the most effective catalysts for ECR. After a brief introduction of the fundamental principles of ECR, we devote the rest of the article on the discussions of various types of nanostructured metallic catalysts, which are categorized by their compositions and working mechanisms. Lastly, strategies for improving reaction efficiency and selectivity are discussed.

(Invited) Development of Molecular Photocathodes Based on Metal Complex Photocatalyst and Their Application for Photoelectrochemical CO2 Reduction in Aqueous Electrolyte

Metal complex photocatalysts are promising candidates in CO2 photo-reduction systems in terms of its high efficiency and selectivity under visible light even in aqueous solution.[1] These systems, however, need the sacrificial reductive additives as electron donor due to the low oxidation power of photosensitizer unit. In this study, we developed novel “molecular” photocathodes consisting of Ru(II)-Re(I) metal complex photocatalyst (RuRe) and p-type semiconductor electrodes for visible-light-driven CO2 reduction (Figure). The application of the molecular photocathodes for photoelectrochemical CO2 reduction in aqueous solution was also examined. RuRe consists of tris-diimine Ru(II) unit as a photosensitizer and tricarbonyl diimine Re(I) unit as a catalyst, and has methylphosphonate anchoring group to adsorb on the electrode surface. p-type NiO electrode was synthesized and hybridized with RuRe to obtain molecular photocathode (RuRe/NiO).[2] This RuRe/NiO photocathode displayed photocathodic responses under the visible light (λex > 460 nm), which selectively photoexcites Ru(II) photosensitizer in RuRe, in a CO2-purged aqueous electrolyte without the need for any sacrificial additives. It reflects that the photo-excited RuRe can receive electrons from an external circuit through the NiO electrode. The onset potential for cathodic photocurrent was approx. -0.1 V vs. Ag/AgCl in a CO2-purged 50 mM NaHCO3 aqueous solution. Photoelectrochemical CO2 reduction using the RuRe/NiO photocathode was examined under the continuous irradiation at the potential of -0.7 V vs. Ag/AgCl, resulting that the catalytic amount of CO was observed. Its turnover number for CO formation, which was based on the amount of RuRe on the NiO, was 32 for 12 h irradiation. These results clearly suggest that the immobilized metal complex photocatalyst (RuRe) functions to drive photoreduction of CO2 with using electrons supplied from the NiO electrode. We next developed p-type CuGaO2 electrode as an alternative of NiO for such molecular photocathode with RuRe.[3] The resulting RuRe/CuGaO2 photocathode also shows photoelectrochemical activity for CO2 reduction under visible light irradiation. The photocathodic responses was obtained from approx. +0.3 V vs. Ag/AgCl, which is equivalent to +0.9 V vs. RHE. This value of onset potential is around 0.4 V positive than that for RuRe/NiO, which means that the utilization of CuGaO2 as an electrode material enlarged the region of working potential for CO2 reduction to positive direction. This tendency agreed well to the flat band potentials of these semiconductor electrodes obtained from the electrochemical impedance spectroscopy. The turnover number of CO formation using the RuRe/CuGaO2 photocathode reached to 125 for 15 h irradiation, while H2 was also generated as byproduct. These results indicate the advantage of CuGaO2 for usage of an electrode material for molecular photocathode from the aspect of efficient interfacial electron injection. In addition, these photocathodes were investigated to combine with a CoO x /TaON photoanode for the oxidation of water.[4] The constructed photoelectrochemical cells consisting of these molecular photocathodes and the CoO x /TaON photoanode enabled the visible-light-driven catalytic reduction of CO2 with water oxidation to obtain CO and O2 as the products. These systems successfully demonstrated CO2 reduction using water as an electron donor by means of combined photocatalytic abilities of both the molecular metal complex (RuRe) and the semiconductor material (TaON). To the best of our knowledge, these are the sole examples of visible-light-driven CO2 reduction systems using water as the reductant, based on molecular photocatalysts with hybridizing semiconductor. [1] Y. Yamazaki, H. Takeda and O. Ishitani, J. Photochem. Photobiol. C, 2015, 25, 106–137.; A. Nakada, K. Koike, K. Maeda and O. Ishitani, Green Chem., 2016, 18, 139–143. [2] G. Sahara, R. Abe, M. Higashi, T. Morikawa, K. Maeda, Y. Ueda and O. Ishitani, Chem. Commun., 2015, 51, 10722–10725.; G. Sahara, H. Kumagai, K. Maeda, N. Kaeffer, V. Artero, M. Higashi, R. Abe and O. Ishitani, J. Am. Chem. Soc., 2016, 138, 14152–14158. [3] H. Kumagai, G. Sahara, K. Maeda, M. Higashi, R. Abe and O. Ishitani, Chem. Sci., 2017, 8, 4242–4249. [4] M. Higashi, K. Domen and R. Abe, J. Am. Chem. Soc., 2012, 134, 6968–6971. Figure 1

Cu2O-tipped ZnO nanorods with enhanced photoelectrochemical performance for CO2 photoreduction

The design of Cu2O-tipped ZnO nanorods is proposed here aiming at enhanced photoelectrochemical properties. The tip-selective deposition of Cu2O is confirmed by scanning transmission electron microscopy (STEM). The photoinduced charge behavior like charge generation, separation and transport has been thoroughly studied by UV–vis absorption analysis and different photoelectrochemical characterizations, including transient photocurrent, incident photon-to-current efficiency (IPCE), electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent spectroscopy (IMPS), and Mott-Schottky measurements. The photoelectrochemical characterizations clearly indicate that ZnO/Cu2O structures exhibit much higher performance than pristine ZnO, due to the formation of p-n junction, as well as the tip selective growth of Cu2O on ZnO. Photocatalytic CO2 reduction in aqueous solution under UV-visible light illumination shows that CO is the main product, and with the increase of the Cu2O content in the heterostructure, the CO yield increases. This work shows that Cu2O-tipped ZnO nanorods possess improved behavior of charge generation, separation and transport, which may work as a potential candidate for photocatalytic CO2 reduction.

Shape-controlled bismuth nanoflakes as highly selective catalysts for electrochemical carbon dioxide reduction to formate

Nanostructured bismuth (Bi) nanoflakes were designed and directly grown on Cu substrate using a novel pulse electrodeposition method. Compared with conventional bismuth film grown by direct current electrodeposition, Bi nanoflakes have large number of edge and corner sites. As it has been proven by numerical simulation, sharp edge or corner sites of the nanostructures form strong local electric fields, which boost the catalytic activity for the electrochemical reduction of CO2 in aqueous solution. The Bi nanoflakes showed a high HCOO- faradaic efficiency (FE = 79.5%) at low potential of −0.4 VRHE and achieved a maximum FE close to 100% at −0.6 VRHE, meaning that the shape control of Bi electrocatalyst is indeed an efficient way to reduce the electrical power consumption for HCOO- production. Moreover, Bi nanoflakes were stable during 10h operation in 0.1M KHCO3 aqueous solution. The results suggest that tailoring the nanostructure is a key in developing a high performance noble-metal-free electrocatalyst for electrochemical CO2 reduction in aqueous solution.

CO2 electroreduction at AuxCu1-x obtained by pulsed laser deposition in O2 atmosphere

AuxCu1-x thin films were synthesized by pulsed laser deposition (PLD) and their electrocatalytic properties towards CO2 reduction in aqueous solution were assessed. The presence of an O2 atmosphere during the PLD process modified the chemical nature of the resulting AuxCu1-x films, with different oxide types identified by X-ray photoelectron spectroscopy. The impact of these oxides, and of the Cu/Au stoichiometry, on the partial current density and conversion efficiency were assessed. The formation of AuxCu1-x alloy thin films and/or the introduction of an O2 atmosphere during deposition does not yield to any marked increase of the formation of carbonaceous compounds, and CO and H2 were the only two products formed, along with formate detected in trace amounts (<1%). Oxide-derived Au catalysts obtained by PLD under O2 atmosphere do not alter CO2 selectivity towards CO formation. High copper content catalysts deposited in vacuum exhibit the lowest overall CO FE%, while increasing the Au content enhances it. The same trend is observed for AuxCu1-x catalysts deposited under 2 and 220 mTorr O2, aside from the fact that increasing Cu content under high O2 pressure has a less negative influence on CO FE%.

Single-Site, Heterogeneous Electrocatalytic Reduction of CO2 in Water as the Solvent

Creating stable surface-bound molecular catalysts for CO2 reduction in aqueous solutions for either electrochemical or photoelectrochemical reduction is a continuing challenge. We report here the preparation and characterization of thin oxide/carbon nanotube electrodes on fluorine-doped tin oxide (FTO) electrodes. The electrodes were prepared by atomic layer deposition (ALD) of ∼15 nm of TiO2 followed by a layer of carbon nanotubes and a thin (2 nm) overlayer of TiO2 for surface stabilization and binding. The phosphonate-derivatized version of the known aqueous solution catalyst for H2/CO reduction, [RuII(tpy-Ph–CH2–PO3H2)(Mebim-py)(H2O)](PF6)2 (tpy-Ph–CH2–PO3H2 = (4-([2, 2′:6′,2″-terpyridin]-4′-yl)benzyl)phosphonic acid; Mebim-py = 3-methyl-1-pyridyl-benzimidazol-2-ylidene), was added to the surface and stabilized by addition of a thin overlayer of TiO2 by ALD. In the derivatized electrodes, the catalyst maintains its reactivity toward CO2 reduction in the short-term, giving mixtures of H2/CO that vary f...

Cu-CDots nanocorals as electrocatalyst for highly efficient CO2 reduction to formate.

Electrochemical reduction of CO2 is a key component of many prospective artificial technologies for renewable carbon-containing fuels, but it still suffers from the high overpotentials required to drive the process, low selectivity for diversiform products and the high cost of the catalyst. Here, we report that Cu-CDots nanocorals is a highly efficient, low-cost and stable electrocatalyst for CO2 reduction in aqueous solution. The major product of CO2 reduction on the Cu-CDots nanocorals is HCOOH with an inconceivable low overpotential of 0.13 V and a high Faraday efficiency of 79% at a moderate potential of -0.7 V vs. RHE. In the present system, CDots can increase the adsorption capacity of CO2 molecules and H+, which play important roles in CO2 reduction. The high selectivity of HCOOH for CO2 reduction may be ascribed to that CDots can greatly diminish the HCOOH desorption energy and improve the catalytic selectivity for HCOOH. Furthermore, Cu-CDots nanocorals exhibit a long-term stability during 5 h-electrolysis.