Faradaic Current Density Research Articles

Regulation of coordinated nitrogen species for atomically dispersed Fe-N5 catalyst to boost electrocatalytic CO2-to-CO conversion

Single atom Fe catalysts coordinated with five N atoms (Fe-N5) have been adopted for excellent CO2-to-CO conversion. However, Fe-N5 catalysts typically face trade-offs among Faradaic efficiency (FE), current density, and stability, posing challenges for further commercialization. Additionally, the role of coordinated N species in their catalytic activities remains unclear. Herein, Fe-N5 catalysts coordinated with a high abundance of pyridinic-N (Fe-N5-pyri) or pyrrolic-N (Fe-N5-pyrro) are synthesized. Both operando experiment results and theoretical calculation manifest that pyrrolic-N increases CO2 adsorption capacity, reduces the reaction free energies required for CO2 activation, and facilitates *CO desorption by weakening the bonding strength with reaction centers. As a result, Fe-N5-pyrro exhibits superior CO2-to-CO conversion performance, achieving a maximum FECO of 96.6% and a partial current density exceeding –130mAcm-2 in 0.5M KHCO3, maintaining stable operation for over 100h. This work highlights the role of nitrogen species in Fe-N5 catalysts and provides a promising strategy for synthesizing robust catalyst for CO2 electrochemical reduction.

A Nitrogen- and Carbon-Present Tin Dioxide-Supported Palladium Composite Catalyst (Pd/N-C-SnO2)

For the first time, nitrogen- and carbon-present tin dioxide-supported palladium composite catalysts (denoted as Pd/N-C-SnO2) were prepared via an HCH method (HCH is the abbreviation for the hydrothermal process–calcination–hydrothermal process preparation process). In this work, firstly, three catalyst carriers (denoted as cc) were prepared using a hydrothermal-process-aided calcination method, and catalyst carriers prepared using ammonia monohydrate (NH3∙H2O), N,N-dimethylformamide (C3H7NO) and triethanolamine (C6H15NO3) as the nitrogen sources were nominated as cc1, cc2 and cc3, respectively. Secondly, these catalyst carriers were reacted with palladium oxide monohydrate (PdO·H2O) hydrothermally to generate catalysts c1, c2 and c3. As testified by XRD and XPS, besides carbon materials and the N-containing substances, the main substances of all prepared catalysts were SnO2 and metallic palladium (Pd). Above all things, all resultant catalysts, especially c2, showed a prominent electrocatalytic activity towards the ethanol oxidation reaction (EOR). As indicated by the CV (cyclic voltammetry) results, all fabricated catalysts presented a clear electrocatalytic activity towards the EOR. In the CA (chronoamperometry) measurement, the faradaic current density of EOR measured on c2 at −0.27 V vs. an SCE (saturated calomel electrode) after 7200 s was still maintained at about 5.6 mA cm−2. Preparing a novel catalyst carrier, N-C-SnO2, and preparing a new EOR catalyst, Pd/N-C-SnO2, were the principal dedications of this preliminary work, which was very beneficial to the development of Pd-based EOR catalysts.

A simulation-based analysis of optical read-out for electrochemical reactions using composite vortex beams.

We propose an optical read-out method for extracting faradaic current in electrochemical (EC) reactions and analyze its performance using opto-EC simulations. Our approach utilizes structured electrodes to generate composite optical vortex (COV) beams upon optical illumination. Through opto-EC simulations, we demonstrate that the EC reaction of 10 mM potassium ferricyanide induces a refractive index (RI) change, RI, of approximately RI units, leading to the rotation of the COV beam's intensity profile with a peak rotation of . This rotation's magnitude is proportional to RI, while the rate correlates with the faradaic current ( ) density responsible for RI. As the opto-EC information is from bulk RI, it remains unaffected by interfering non-faradaic components at the interface and is advantageous for studying intermediate species and bulk homogeneous reactions. Furthermore, as rotation depends on density rather than itself, this method proves beneficial in low scenarios, such as when employing micro-electrodes to decrease solution resistance or obtain localized EC data. Even in low density scenarios, like monitoring slow EC reactions, our method enables signal amplification by accumulating rotation over time. This interdisciplinary approach holds promise for advancing EC research and addressing critical challenges across various fields, including energy storage, corrosion protection, environmental remediation, and biomedical sciences.

Multivalent Cu sites synergistically adjust carbonaceous intermediates adsorption for electrocatalytic ethanol production

Copper (Cu)-based catalysts show promise for electrocatalytic CO2 reduction (CO2RR) to multi-carbon alcohols, but thermodynamic constraints lead to competitive hydrocarbon (e.g., ethylene) production. Achieving selective ethanol production with high Faradaic efficiency (FE) and current density is still challenging. Here we show a multivalent Cu-based catalyst, Cu-2,3,7,8-tetraaminophenazine-1,4,6,9-tetraone (Cu-TAPT) with Cu2+ and Cu+ atomic ratio of about 1:2 for CO2RR. Cu-TAPT exhibits an ethanol FE of 54.3 ± 3% at an industrial-scale current density of 429 mA cm−2, with the ethanol-to-ethylene ratio reaching 3.14:1. Experimental and theoretical calculations collectively unveil that the catalyst is stable during CO2RR, resulting from suitable coordination of the Cu2+ and Cu+ with the functional groups in TAPT. Additionally, mechanism studies show that the increased ethanol selectivity originates from synergy of multivalent Cu sites, which can promote asymmetric C–C coupling and adjust the adsorption strength of different carbonaceous intermediates, favoring hydroxy-containing C2 intermediate (*HCCHOH) formation and formation of ethanol.

Highly Efficient Electrosynthesis of Urea from CO2 and Nitrate by a Metal‐Organic Framework with Dual Active Sites

Electrosynthesis of urea from CO2 and NO3− is a sustainable alternative to energy‐intensive industrial processes. The challenge hindering the progress is the development of advanced electrocatalysts that yield urea with both high Faradaic efficiency (FE) and current density. In this work, we designed a new two‐dimensional MOF, namely PcNi−Fe−O, constructed by nickel‐phthalocyanine (NiPc) ligands and square‐planar FeO4 nodes. PcNi−Fe−O exhibits remarkable performance to yield urea at a high current density of 10.1 mA cm−2 with a high FE(urea) of 54.1% in a neutral aqueous solution, surpassing those of most reported electrocatalysts. No obvious performance degradation was observed over 20 hours of continuous operation at the current density of 10.1 mA cm−2. By expanding the electrode area to 25 cm2 and operating for 8 hours, we obtained 0.164 g of high‐purity urea, underscoring its potential for industrial applications. Mechanism study unveiled the enhanced performance might be ascribed to the synergistic interaction between NiPc and FeO4 sites. Specifically, NH3 produced at the FeO4 site can efficiently migrate and couple with the *NHCOOH intermediate adsorbed on the urea‐producing site (NiPc). This synergistic effect results in a lower energy barrier for C−N bond formation than those of the reported catalysts with single active sites.

Highly Efficient Electrosynthesis of Urea from CO2 and Nitrate by a Metal-Organic Framework with Dual Active Sites.

Electrosynthesis of urea from CO2 and NO3 - is a sustainable alternative to energy-intensive industrial processes. The main challenge hindering the progress of this technology lies in the development of advanced electrocatalysts that efficiently utilize abundant, low-cost CO2 and nitrogen sources to yield urea with both high Faradaic efficiency (FE) and current density. In this work, we designed and prepared a new two-dimensional metal-organic framework (MOF), namely PcNi-Fe-O, constructed by nickel-phthalocyanine (NiPc) ligands and square-planar FeO4 nodes, as the electrocatalyst for urea electrosynthesis. PcNi-Fe-O exhibits remarkable performance to yield urea at a high current density of 10.1 mA cm-2 with a high FE(urea) of 54.1 % in a neutral aqueous solution, surpassing those of most reported electrocatalysts. No obvious performance degradation was observed over 20 hours of continuous operation at the current density of 10.1 mA cm-2. By expanding the electrode area to 25 cm2 and operating for 8 hours, we obtained 0.164 g of high-purity urea, underscoring its potential for industrial applications. Mechanism study unveiled the enhanced performance might be ascribed to the synergistic interaction between NiPc and FeO4 sites. Specifically, NH3 produced at the FeO4 site can efficiently migrate and couple with the *NHCOOH intermediate adsorbed on the urea-producing site (NiPc). This synergistic effect results in a lower energy barrier for C-N bond formation than those of the reported catalysts with single active sites.

Surface nitrided CuBi2O4 electrocatalysts with excellent selectivity for CO2 reduction to methanol

Developing a high-performance electrocatalyst for converting CO2 into methanol is of utmost importance. However, poor selectivity, and unavoidable competitive hydrogenolysis reaction (HER) are still challenges to be solved. In this study, a surface nitrided strategy was designed to synthesize a series N-copper-bismuth bimetallic oxide electrocatalysts (NCBO-t, t = 1, 2, 4 h) for CO2RR. The electrocatalyst NCBO-2 demonstrated a selectivity for methanol reaching 86.43 %, along with an impressive long-term stability lasting for 11 h, all achieved at a relatively low potential of −0.9 V. Experimental results and density functional theory (DFT) calculations indicated the introduction of nitrogen facilitates methanol production by optimizing binding of the reaction intermediate *OCH while promotes Faradaic efficiency of methanol products by suppressing the competitive HER, resulting in high Faradaic efficiency, current density, and stability of CO2RR at low overpotentials. This study offers a feasible idea for synthesis of high-performance CO2 methanol by electroreduction.

Single-atomic-Ni electrocatalyst derived from phthalocyanine-modified MOF for convoying CO2 intelligent utilization

Single-atomic-site catalysts have been demonstrated as promising candidates for electrochemical CO2 reduction reaction (eCO2RR). However, the universal construction strategies need to be further developed to synthesize the desired single-atomic-site catalysts with high eCO2RR activity for feasible CO2 utilization. Herein, a novel 2-methylimidazole-phthalocyanine-Ni (IM4NiPc) coordinatively modified ZIF-8 was rationally fabricated and applied to derive the single-atomic-Ni electrocatalyst (Ni-N-C-l), which is capable of delivering much improved activity for eCO2RR, compared to the pristine IM4NiPc immobilized onto ZIF-8-derived N-doped carbon surface, and is also comparable to the best reported catalysts. The satisfied Faradaic efficiency, current density and stability of CO2-to-CO electroconversion over Ni-N-C-l are shown to originate from the verified Ni-N4 configuration, particularly, reaching a CO Faradaic efficiency of 99% in a wide potential range. Moreover, based on the outstanding eCO2RR activity of Ni-N-C-l, we successfully realized the exemplary synthesis of amide polymer materials through CO-mediated electro/thermocatalytic cascade processes, demonstrating the feasibility of utilizing CO2 for material manufacturing. This finding is expected to provide useful insight on the precise design and rational synthesis of the novel single-atomic-site catalysts for future CO2 intelligent utilization.

Revealing the Lattice Carbonate Mediated Mechanism in Cu2(OH)2CO3 for Electrocatalytic Reduction of CO2 to C2H4.

Understanding the CO2 transformation mechanism on materials is essential for the design of efficient electrocatalysts for CO2 reduction. In aconventional adsorbate evolution mechanism (AEM), the catalysts encounter multiple high-energy barrier steps, especially CO2 activation, limiting the activity and selectivity. Here, lattice carbonate from Cu2(OH)2CO3 is revealed to be a mediator between CO2 molecules and catalyst during CO2 electroreduction by a 13C isotope labeling method, which can bypass the high energy barrier of CO2 activation and strongly enhance the performance. With the lattice carbonate mediated mechanism (LCMM), the Cu2(OH)2CO3 electrode exhibited ten-fold faradaic efficiency and 15-fold current density for ethylene production than the Cu2O electrode with AEM at a low overpotential. Theoretical calculations and in situ Raman spectroscopy results show that symmetric vibration of carbonate is precisely enhanced on the catalyst surface with LCMM, leading to faster electron transfer, and lower energy barriers of CO2 activation and carbon-carbon coupling. This work provides a route to develop efficient electrocatalysts for CO2 reduction based on lattice-mediated mechanism.

Tailoring Interfaces for Enhanced Methanol Production from Photoelectrochemical CO2 Reduction.

Efficient and stable photoelectrochemical reduction of CO2 into highly reduced liquid fuels remains a formidable challenge, which requires an innovative semiconductor/catalyst interface to tackle. In this study, we introduce a strategy involving the fabrication of a silicon micropillar array structure coated with a superhydrophobic fluorinated carbon layer for the photoelectrochemical conversion of CO2 into methanol. The pillars increase the electrode surface area, improve catalyst loading and adhesion without compromising light absorption, and help confine gaseous intermediates near the catalyst surface. The superhydrophobic coating passivates parasitic side reactions and further enhances local accumulation of reaction intermediates. Upon one-electron reduction of the molecular catalyst, the semiconductor-catalyst interface changes from adaptive to buried junctions, providing a sufficient thermodynamic driving force for CO2 reduction. These structures together create a unique microenvironment for effective reduction of CO2 to methanol, leading to a remarkable Faradaic efficiency reaching 20% together with a partial current density of 3.4 mA cm-2, surpassing the previous record based on planar silicon photoelectrodes by a notable factor of 17. This work demonstrates a new pathway for enhancing photoelectrocatalytic CO2 reduction through meticulous interface and microenvironment tailoring and sets a benchmark for both Faradaic efficiency and current density in solar liquid fuel production.

Synergistic catalytic conversion of nitrate into ammonia on copper phthalocyanine and FeNC two-component catalyst

Cu-based catalysts have been extensively studied to enhance the performance of the electrochemical nitrate reduction reaction (NO3–RR), while it is still a challenge to balance high ammonia (NH3) current density and Faradaic efficiency. Here, we incorporated nitrogen coordinated iron single atom catalyst (FeNC) with copper phthalocyanine (CuPc), denoted as CuPc/FeNC, for NO3–RR. Compared with the two individual catalysts, this two-component catalyst increases NH3 Faradaic efficiency and current density at low overpotentials, achieves efficient synergistic catalytic conversion. Experiments and theoretical calculations reveal that the enhanced electrochemical performance of CuPc/FeNC catalyst comes from the tandem process, in which NO2– is produced on CuPc and then transferred to FeNC and further reduced to NH3. In this exceptional tandem catalyst system, an outstanding NH3 Faradaic efficiency close to 100% was achieved at potentials greater than –0.35 V vs. RHE, coupled with a peak NH3 partial current density of 273 mA cm–2 at –0.57 V vs. RHE, effectively suppressing NO2– production across the entire potential range. This strategy provides a design platform for the continued advancement of NO3–RR catalysts.

Reactant enrichment in yolk-shell structured Pd/TiN nanoreactors for boosting electrocatalytic hydrodechlorination performance

Enhancing the enrichment behavior of low-concentration chlorinated organic pollutants remains a significant challenge in electrocatalytic hydrodechlorination (EHDC) technology. Metal-loaded hollow nanoarchitecture has emerged as a promising nanoreactor to improve reaction enrichment behavior because of its tailorable microenvironments and electronic properties. Herein, a structural engineering strategy is developed to synthesize yolk-shell structured TiN spheres supported Pd nanoreactors (Pd/YS-TiN) with confined mesoscopic spaces. Characterization by multiple techniques reveals that the yolk-shell structure of YS-TiN, with high specific surface area (139.0 m2/g) and appropriately mesoporosity (6.9 nm), exposes numerous Pd nanoparticles (∼4.0 nm) on outer/inner surface of the shell and yolk-core solid sphere, ensuring an efficient utilization of active sites for enhancing the 2,4-DCP detoxification. Consequently, the structurally optimized Pd/YS-TiN nanoreactor consistently displays maximum reaction kinetics, dechlorination degree, faradaic current density, H* utilization and product selectivity, surpassing hollow TiN-supported Pd and Pd/C catalysts. The super EHDC performance of 91.8 % 2,4-DCP conversion, a specific activity of 1.68 min−1 molPd−1, and a mass activity of 6.06 min−1 gPd−1 is obtained at −0.85 V and 180 min, outperforming most reported catalysts. Combining experimental and density functional theory results, the exceptional reaction enrichment behavior of Pd/YS-TiN originates from (1) alleviating the overstrong adsorption of product phenol through strong metal-support interactions and (2) enhancing mass transport efficiency facilitated by the local concentration gradient and mesoporous shell. This study elucidates how metal-support interactions and mass transport synergistically enhance reaction enrichment behavior, showcasing potential benefits in environmental remediation applications.

Enhancing Local CO2 Adsorption by L-histidine Incorporation for Selective Formate Production Over the Wide Potential Window.

Electrochemical carbon dioxide reduction reaction (CO2 RR) to produce valuable chemicals is a promising pathway to alleviate the energy crisis and global warming issues. However, simultaneously achieving high Faradaic efficiency (FE) and current densities of CO2 RR in a wide potential range remains as a huge challenge for practical implements. Herein, we demonstrate that incorporating bismuth-based (BH) catalysts with L-histidine, a common amino acid molecule of proteins, is an effective strategy to overcome the inherent trade-off between the activity and selectivity. Benefiting from the significantly enhanced CO2 adsorption capability and promoted electron-rich nature by L-histidine integrity, the BH catalyst exhibits excellent FEformate in the unprecedented wide potential windows (>90 % within -0.1--1.8 V and >95 % within -0.2--1.6 V versus reversible hydrogen electrode, RHE). Excellent CO2 RR performance can still be achieved under the low-concentration CO2 feeding (e.g., 20 vol.%). Besides, an extremely low onset potential of -0.05 VRHE (close to the theoretical thermodynamic potential of -0.02 VRHE ) was detected by in situ ultraviolet-visible (UV-Vis) measurements, together with stable operation over 50 h with preserved FEformate of ≈95 % and high partial current density of 326.2 mA cm-2 at -1.0 VRHE .

Evolution of bismuth oxide catalysts during electrochemical CO2 reduction

Bismuth is a promising electrocatalyst for active and selective CO2 electroreduction to formate. Herein, we investigated the evolution of various Bi-based catalysts (β-Bi2O3 nanoparticles, BiOBr nanosheets, Bi2O2CO3 nanosheets, and large α-Bi2O3 and β-Bi2O3 particles) during reaction. Apart from the α-Bi2O3 particles, all the electrocatalysts reach the same Faradaic efficiency (93 ± 2%) and current density during potentiostatic operation, and their morphology changed to nanosheets. This change in morphology can be linked to the formation of Bi2O2CO3 layers, which are prone to reduction to metallic Bi. The final phase and morphology depend on the size of the Bi precursor. Quasi-in situ XPS suggests that a Bi2O2CO3 contribution persists on the surface even for the reduced catalysts. At a current density of 200 mA/cm2, all catalysts reduce to metallic Bi without forming a well-defined sheet morphology. Only for the Bi2O3 nanoparticles can a FE above 90% be maintained.

Boosting the electrochemical CO2 reduction performance by Cu2O/β-Bi2O3 bimetallic heterojunction with the assistance of light

CO2, as one of the greenhouse gases, actually represents a cheap and abundant C1 fuel to produce fuels and chemical stocks. Herein, inspired by photocatalysis and electrocatalysis, we have successfully synthesized a series of copper and bismuth oxides with heterostructure by a first co-electrodeposition method and then by thermal treatment at different temperatures. The bimetallic oxide (Cu2O/β-Bi2O3) at 300 °C with the main exposure of β-Bi2O3 (201) planes shows the beautiful micro-flower morphology with numerous petals in thickness around 20 ∼ 40 nm. Therefore, the Cu2O/β-Bi2O3 heterostructure with active edge sites can electrochemically convert CO2 into formate with a promising Faradaic efficiency (96.3 %) and current density (40.4 mA cm−2) at − 0.97 V vs. RHE. Specifically, the current density of Cu2O/β-Bi2O3 bimetallic catalyst can be largely enhanced to 48.5 mA cm−2 at − 0.92 V vs. RHE with the assistance of light compared to the 30.1 mA cm−2 without light. The production rate of formate with the assistance of light can also be increased to 705.1 μmol h−1 cm−2, superior to that of 536.4 μmol h−1 cm−2 without light. Such an excellent photo-assisted electrochemical CO2 reduction performance is due to the fast charge-transfer process between Cu2O and β-Bi2O3. This study may provide a new route to directly synthesize the photoactive electrocatalysts with more edge sites and heterojunction for promoting electrochemical CO2 reduction performance with the assistance of light field.

Boron-induced growth of highly textured Ag (1 1 1) films with nano-tentacle structures for the electrochemical reduction of CO2 to CO

Ag is a cost-effective alternative to Au as a catalyst for the electrochemical reduction of CO2 into CO, but a reduction in the accompanying overpotential is required to make Ag viable. In this study we use B to modulate the catalytic performance of Ag towards the electrochemical reduction of CO2 to CO. Initial DFT simulations discloses a deviation from the linear scaling relations with the inclusion of B that stabilizes the *COOH intermediate while weakening the binding strength of *CO. A magnetron co-sputtering process is used to develop a catalyst based on B-induced crystal growth of highly textured Ag (111) films. Incorporation of B facilitates the formation of Ag (111) coherent twin boundaries, which gives rise to unique nano-tentacle structures. The Ag-B catalyst achieves a faradaic efficiency of CO production of 97.9% at −0.9 V vs RHE with a partial current density that is four times higher compared to pristine Ag. Thus, the inclusion of B into Ag offers a facile approach for circumventing the linear scaling relations, allowing for the design of electrocatalysts with high faradaic efficiencies and current densities.

Promoting CO2 Electroreduction to Multi‐Carbon Products by Hydrophobicity‐Induced Electro‐Kinetic Retardation

AbstractAdvancing the performance of the Cu‐catalyzed electrochemical CO2 reduction reaction (CO2RR) is crucial for its practical applications. Still, the wettable pristine Cu surface often suffers from low exposure to CO2, reducing the Faradaic efficiencies (FEs) and current densities for multi‐carbon (C2+) products. Recent studies have proposed that increasing surface availability for CO2 by cation‐exchange ionomers can enhance the C2+ product formation rates. However, due to the rapid formation and consumption of *CO, such promotion in reaction kinetics can shorten the residence of *CO whose adsorption determines C2+ selectivity, and thus the resulting C2+ FEs remain low. Herein, we discover that the electro‐kinetic retardation caused by the strong hydrophobicity of quaternary ammonium group‐functionalized polynorbornene ionomers can greatly prolong the *CO residence on Cu. This unconventional electro‐kinetic effect is demonstrated by the increased Tafel slopes and the decreased sensitivity of *CO coverage change to potentials. As a result, the strongly hydrophobic Cu electrodes exhibit C2+ Faradaic efficiencies of ≈90 % at a partial current density of 223 mA cm−2, more than twice of bare or hydrophilic Cu surfaces.

Promoting CO2 Electroreduction to Multi-Carbon Products by Hydrophobicity-Induced Electro-Kinetic Retardation.

Advancing the performance of the Cu-catalyzed electrochemical CO2 reduction reaction (CO2 RR) is crucial for its practical applications. Still, the wettable pristine Cu surface often suffers from low exposure to CO2 , reducing the Faradaic efficiencies (FEs) and current densities for multi-carbon (C2+ ) products. Recent studies have proposed that increasing surface availability for CO2 by cation-exchange ionomers can enhance the C2+ product formation rates. However, due to the rapid formation and consumption of *CO, such promotion in reaction kinetics can shorten the residence of *CO whose adsorption determines C2+ selectivity, and thus the resulting C2+ FEs remain low. Herein, we discover that the electro-kinetic retardation caused by the strong hydrophobicity of quaternary ammonium group-functionalized polynorbornene ionomers can greatly prolong the *CO residence on Cu. This unconventional electro-kinetic effect is demonstrated by the increased Tafel slopes and the decreased sensitivity of *CO coverage change to potentials. As a result, the strongly hydrophobic Cu electrodes exhibit C2+ Faradaic efficiencies of ≈90 % at a partial current density of 223 mA cm-2 , more than twice of bare or hydrophilic Cu surfaces.

Machine Learning Assisted Analysis of Electrochemical H2O2 Production

The two-electron water oxidation reaction (2e– WOR) provides an option for on-site production of the valuable chemical hydrogen peroxide (H2O2). A major challenge for the 2e– WOR is the need to improve its selectivity toward H2O2 over O2 production through the oxygen evolution reaction. Electrolyte engineering has shown great promise in improving the selectivity and production rates toward H2O2. However, experimental efforts in optimizing the electrolyte only yield results at discrete conditions, which does not provide a complete picture of performance over the entire parameter range. Here, we apply a machine learning assisted prediction to map out the performance of electrochemical H2O2 production over the continuous parameter space of electrolyte composition and applied potential. We collected experimental data of faradaic efficiencies (FEH2O2) and current densities toward H2O2 (JH2O2) as functions of the applied potential and carbonate ion mole fractions (HCO3– and CO32–) in the electrolyte. The data were then used to train a support vector regression model with 5-fold cross-validation. The accuracy of the model was verified against additional experimental results. The model identified that a maximum H2O2 current density of 2.16 mA/cm2 can be achieved from an optimized bicarbonate ion mole fraction of 0.225 at an applied potential of 3.25 V vs RHE. Lastly, the continuous model enables us to evaluate the thermal efficiency, H2O2 electricity cost, and time needed to produce a set amount of H2O2 over a broad range of electrolytes and applied potential conditions. This work demonstrates how machine learning enables the use of discrete experimental points to construct a continuous picture of electrochemical H2O2 production with high accuracy.

Electrocatalytic reduction of carbon dioxide in confined microspace utilizing single nickel atom decorated nitrogen-doped carbon nanospheres

Carbon dioxide electroreduction reaction (CO2RR), as a rational regulation of CO2 resource utilization, demands effectively selective catalysts for converting CO2 into high-value-added chemicals. Carbon-based nanoreactors featuring rationally designed porous framework structures might provide a unique chemical environment for confining and stabilizing the active metal species, consequently improving the CO2RR activity. Herein, nitrogen-doped porous carbon nanospheres decorated by single Ni atom (Ni-NCN) featuring a Ni-N4 structure were synthesized using the modified sol-gel method for the reduction of CO2 to CO. The synergistic effect of the Ni-N4 active sites homogenously distributed in the interconnected pore structure and the favorable chemical confined microspace of carbon nanospheres endows it with excellent CO2RR activity. In the H- type cell, Ni-NCN displays a CO Faradaic efficiency up to 96.6 % and a CO current density of 9.8 mA cm−2 at − 0.83 V (vs. RHE), as well as a high turnover frequency (TOF) of 10658 h−1 at − 1.33 V (vs. RHE). In the flow cell, the mass transfer can be further facilitated by the formation of three-phase interface. The Faradaic efficiency and current density of CO2RR catalyzed by Ni-NCN is enhanced to 97.9 % and 102.4 mA cm−2 at − 1.13 V (vs. RHE), and the wide potential window ranges from − 0.53 V to − 1.33 V (vs. RHE) with the Faradaic efficiency more than 95 %. Density functional theory (DFT) calculations reveal that the high selectivity of Ni-N4 sites is mainly ascribed to the high energy barrier that restrains the hydrogen evolution reaction (HER). Meanwhile, the lower CO binding energy on Ni-N4 site helps the escape of CO to increase the TOF of active sites. The in-situ Fourier transform infrared (FTIR) spectroscopy verifies that the intermediate *COOH can be more stable in the confined environment of Ni-NCN to promote the selectivity of CO2RR. The strategy of constructing confined microspace paves a new path for the rational design of high-efficient single atom catalysts for CO2 reduction.