Anodic Current Research Articles

High yield electrosynthesis of oxygenates from CO using a relay Cu-Ag co-catalyst system

As a sustainable alternative to fossil fuel-based manufacture of bulk oxygenates, electrochemical synthesis using CO and H2O as raw materials at ambient conditions offers immense appeal. However, the upscaling of the electrosynthesis of oxygenates encounters kinetic bottlenecks arising from the competing hydrogen evolution reaction with the selective production of ethylene. Herein, a catalytic relay system that can perform in tandem CO capture, activation, intermediate transfer and enrichment on a Cu-Ag composite catalyst is used for attaining high yield CO-to-oxygenates electrosynthesis at high current densities. The composite catalyst Cu/30Ag (molar ratio of Cu to Ag is 7:3) enables high efficiency CO-to-oxygenates conversion, attaining a maximum partial current density for oxygenates of 800 mA cm−2 at an applied current density of 1200 mA cm−2, and with 67 % selectivity. The ability to finely control the production of ethylene and oxygenates highlights the principle of efficient catalyst design based on the relay mechanism.

Pure-Water-Fed Forward-Bias Bipolar Membrane CO2 Electrolyzer.

Coupling renewable electricity to reduce carbon dioxide (CO2) electrochemically into carbon feedstocks offers a promising pathway to produce chemical fuels sustainably. While there has been success in developing materials and theory for CO2 reduction, the widespread deployment of CO2 electrolyzers has been hindered by challenges in the reactor design and operational stability due to CO2 crossover and (bi)carbonate salt precipitation. Herein, we design asymmetrical bipolar membranes assembled into a zero-gap CO2 electrolyzer fed with pure water, solving both challenges. By investigating and optimizing the anion-exchange-layer thickness, cathode differential pressure, and cell temperature, the forward-bias bipolar membrane CO2 electrolyzer achieves a CO faradic efficiency over 80% with a partial current density over 200 mA cm-2 at less than 3.0 V with negligible CO2 crossover. In addition, this electrolyzer achieves 0.61 and 2.1 mV h-1 decay rates at 150 and 300 mA cm-2 for 200 and 100 h, respectively. Postmortem analysis indicates that the deterioration of catalyst/polymer-electrolyte interfaces resulted from catalyst structural change, and ionomer degradation at reductive potential shows the decay mechanism. All these results point to the future research direction and show a promising pathway to deploy CO2 electrolyzers at scale for industrial applications.

Switching CO2 Electroreduction toward Ethanol by Delocalization State-Tuned Bond Cleavage.

The electrochemical CO2 reduction reaction by copper-based catalysts features a promising approach to generate value-added multicarbon (C2+) products. However, due to the unfavored formation of oxygenate intermediates on the catalyst surface, the selectivity of C2+ alcohols like ethanol remains unsatisfactory compared to that of ethylene. The bifurcation point (i.e., the CH2═CHO* intermediate adsorbed on Cu via a Cu-O-C linkage) is critical to the C2+ product selectivity, whereas the subsequent cleavage of the Cu-O or the O-C bond determines the ethanol or ethylene pathway. Inspired by the hard-soft acid-base theory, in this work, we demonstrate an electron delocalization tuning strategy of the Cu catalyst by a nitrene surface functionalization approach, which allows weakening and cleaving of the Cu-O bond of the adsorbed CH2═CHO*, as well as accelerating hydrogenation of the C═C bond along the ethanol pathway. As a result, the nitrene-functionalized Cu catalyst exhibited a much-enhanced ethanol Faradaic efficiency of 45% with a peak partial current density of 406 mA·cm-2, substantially exceeding that of unmodified Cu or amide-functionalized Cu. When assembled in a membrane electrode assembly electrolyzer, the catalyst presented a stable CO2-to-ethanol conversion for >300 h at an industrial current density of 400 mA·cm-2.

Investigating the influence of oxygen doping in modulating product distribution for electrocatalytic CO2 reduction reaction

Efficient carbon recycling hinges on a comprehensive understanding of the mechanics behind electrocatalytic carbon dioxide reduction reactions (ECO2RR). Here, we have engineered, in-situ growth of CuO featured on O-doped gCN (COG) and ex-situ growth of CuO on bare gCN (CG) respectively, functioned as platforms fordisengaging the fundamental of ECO2RR. The COG holds substantial capacity compared to CG for efficient conversion of CO2 into hydrocarbons and initiated the C2 product pathway with enlarged faradaic efficiency (FE). The experimental results indicate that the COG enhanced the product conversion of CH3OH (FE = 61.5% ± 0.5), C2H5OH (FE = 24.7% ± 0.5), and HCOO– (FE = 6.1% ± 0.5) at −1.1 V Vs RHE. Meanwhile, the CG exhibited the maximum conversion of CO2 into CH3OH (FE = 56.4% ± 0.5) at the same potential range. For the CG, the partial current density of CH3OH (JCH3OH) is −1.8 mA cm−2, whereas COG exhibited −4.9 mA cm−2. Interestingly, in this ECO2RR, the study of oxygen doping demonstrated that feasible CO2 conversion, due to its affinity towards CO2 and high donor density.

NHC-CDI Ligands Boost Multicarbon Production in Electrocatalytic CO2 Reduction by Increasing Accumulated Charged Intermediates and Promoting *CO Dimerization on Cu.

Copper-based materials exhibit significant potential as catalysts for electrochemical CO2 reduction, owing to their capacity to generate multicarbon hydrocarbons. The molecular functionalization of Cu electrodes represents a simple yet powerful strategy for improving the intrinsic activity of these materials by favoring specific reaction pathways through the creation of tailored microenvironments around the surface active sites. However, despite its success, comprehensive mechanistic insights derived from experimental techniques are often limited, leaving the active role of surface modifiers inconclusive. In this work, we show that N-heterocyclic carbene-carbodiimide-functionalized Cu catalysts display a remarkable activity for multicarbon product formation, surpassing bare Cu electrodes by more than an order of magnitude. These hybrid catalysts operate efficiently using an electrolyzer equipped with a gas diffusion electrode, achieving a multicarbon product selectivity of 58% with a partial current density of ca. -80 mA cm-2. We found that the activity for multicarbon product formation is closely linked to the surface charge that accumulates during electrocatalysis, stemming from surface intermediate buildup. Through X-ray photoelectron spectroscopy, we elucidated the role of the molecular additives in altering the electronic structure of the Cu electrodes, promoting the stabilization of surface CO. Additionally, in situ Raman measurements established the identity of the reaction intermediates that accumulate during electrocatalysis, indicating preferential CO binding on Cu step sites, known for facilitating C-C coupling. This study underscores the significant potential of molecular surface modifications in developing efficient electrocatalysts for CO2 reduction, highlighting surface charge as a pivotal descriptor of multicarbon product activity.

A novel Cu-based covalent organic framework with Cu-N2O2 single sites for efficient CO2 electroreduction to methane

Single-site catalysts (SSCs) are useful for CO2 electroreduction (CO2ER) to methane (CH4), but their selectivities for CH4 are still unsatisfactory due to the lack of efficient active sites. Herein, a novel Cu-based covalent organic framework (CuN2O2-COF) with Cu-N2O2 single sites was synthesized by the Schiff base reaction and used in CO2ER to improve CH4 generation for the first time. Compared with typical SSCs containing Cu-N4 or Cu-O4 sites, CuN2O2-COF exhibited superior CH4 production efficiency in CO2ER: the Faradaic efficiency of CH4 was as high as 85.4%, and the CH4 partial current density reached 313 mA·cm−2 at −1.3 V, which exceeded those of most electrocatalysts reported thus far. Theoretical calculations indicated that compared with the Cu-N4 or Cu-O4 sites in typical SSCs, the new Cu-N2O2 configuration in CuN2O2-COF increased the d‐band center of the Cu sites and enhanced the adsorption of key intermediates (*COOH and *CHO) required for CO2ER to CH4.

Selective Initiation of Corrosion Pits in Stainless Steel Using Scanning Electrochemical Cell Microscopy.

Scanning electrochemical cell microscopy is a useful technique for determining variations in corrosion behavior across a surface. However, the numerous options for experimental parameters and little understanding of their effect on the corroding system render comparisons of results between studies difficult. Herein, we explore changes in corrosion behavior of two martensitic stainless steels, a cast CA6NM and a wrought S41500, as a result of the chosen experimental parameters, including scan rate, approach potential, surface oil immersion, and tip aperture diameter. The study demonstrates that these experimental parameters can be controlled to probe oxide passivation kinetics and single pitting events by changing the surface state and cathodic currents. We measured the pitting and repassivation kinetics of a single pit and determined the compositional change of the Al2O3 inclusion site initiation point. Hundreds of data points were measured within 17 h of experimental time on the stainless steel samples, allowing statistical averages of corrosion and pitting values. This work will open new avenues for fine-tuning various corrosion aspects at the microscale, thereby contributing to a deeper understanding of the corrosion processes and mechanisms of diverse materials.

La-based Transition Metal Oxide Perovskites as Electrocatalysts for Electrochemical Carbon Dioxide Reduction

We report here the feasibility of using LaTMO3-based perovskites (TM = Co, Cr, Fe, Mn, Ni, i.e., non-Cu 3d transition metals) as electrocatalysts for electrochemical CO2 reduction reaction (eCO2RR). Phase pure LaTMO3 perovskites, having TM-ions in multiple oxidation states for all and O-defects for LaFeO3 and LaNiO3, have been synthesized and tested as electrocatalysts for eCO2RR in flow cell type set-up. The above characteristics of the La-TM-oxides have been found to influence the current densities during eCO2RR at the various applied potentials, with favorable effects of the presence of O-defects (as for LaFeO3 and LaNiO3). Upon eCO2RR, both C1 and C2 liquid products have been obtained, including ethanol, with a partial current density of −2.66 mA cm−2 at −1.2 V vs RHE (for LaFeO3). The types of products and the faradic efficiencies have been found to depend on the TM-ion present (in the LaTMO3); in particular, the oxidation state(s), associated O-defect(s) and electronic conductivity. Furthermore, the electrocatalysts have been found to be stable during eCO2RR. Overall, the present work highlights the potential of La-TM-oxide perovskites for usage as stable electrocatalysts for eCO2RR, and also provides insights into the proper selection of “TM” and reaction conditions for obtaining the desired product(s).

Oxygen‐Pinned Ag1In Single‐Atom Alloy for Efficient Electroreduction CO2 to Formate

AbstractCatalytic conversion of CO2 to valuable formate provides a pathway to carbon neutrality. Indium (In), as a promising catalyst, exhibits high selectivity toward formate due to its suitable bonding ability of *OCHO intermediates. However, it still suffers from the CO2 activation and the protonation steps, leading to low activity and productivity. Here, an oxygen‐pinned stabilization AgIn single‐atom alloy (Op‐Ag1In) is presented for efficiently converting CO2 into formate (≈92.03% Faradaic efficiency) with a partial current density of 13 mA cm−2 at −0.95 V vs RHE by using standard H‐type reactor. The Op‐Ag1In electrocatalyst is more effective in converting CO2 to formate because the activated In sites of Op‐Ag1In catalyst regulate CO2 activation and protonation step of CO2RR and formation of sufficient amounts of *OCHO, which are confirmed by in situ spectroscopic and theoretical calculations. The continuous production of formate is showcased at 70 mA cm–2 for 24 h by utilizing a flow cell and Op‐Ag1In.

The Effect of Sulfuric Acid Anodization on the Electrochemical Properties of Aluminum Alloy AlSi10Mg Prepared by Selective Laser Melting

Aluminum alloy, AlSi10Mg, prepared by selective laser melt (SLM) fabrication was anodized in 9.8% sulfuric acid (Type II) at 15 V for a total of 23 min. Experiments were performed to study the potentiostatic anodization process and its effects on the oxide coating morphology, thickness, and electrochemical properties of the alloy. Prior to anodization, the alloy microstructure is composed of aluminum cells encapsulated in a silicon network. Anodizing the abraded and polished AlSi10Mg surface produced a porous oxide layer with a thickness of 5 μm. The oxide coating weight was 698 ± 29 mg/ft2. The oxide coating forms in the aluminum cells that are isolated from one another by the silicon eutectic phase. In electrochemical tests, the anodic and cathodic potentiodynamic polarization currents were suppressed by factors of 15× and 215×, respectively, as compared to the unanodized controls. The data indicate the anodic oxide coating suppresses the cathodic more than the anodic reaction rate. Linear polarization resistance (R p) values increased by 279× after anodization. The corrosion current density values (j corr) decreased by 133× after anodization. Taken together, the electrochemical data indicate the anodic oxide coating (unsealed) increases the corrosion resistance of the SLM alloy by two orders of magnitude.

Analysis of the correlation between GIS partial discharge current waveform and charge quantity with UHF signals

The Ultra-High Frequency (UHF) method, as a crucial technology for online GIS monitoring, struggles with the issue of being unable to accurately reflect the number of partial discharges, which poses a significant challenge for this technique. To examine the relationship between partial discharge waveforms, charge quantity, and UHF signals, a physical field model of partial discharge is developed using finite element simulation software, allowing a comparison of the peak-to-peak values of UHF signals with the parameters of the partial discharge current. Research demonstrates a roughly linear relationship between the peak-to-peak values of UHF signals and the magnitude of the partial discharge current but no definitive connection with the discharge quantity. These significant findings guide the quantitative detection of partial discharges in electrical equipment using the UHF method.

Photoelectrochemical CO2 reduction in tandem photoelectrode cells: Interpretation of apparent photocurrents

Photoelectrochemical reactors harness solar energy to accelerate heterogeneous chemical reactions and reduce power consumption for a given reaction rate. The tandem photoelectrochemical cell design presented here employs a light penetrable TiO2 photoanode||Cu2O photocathode configuration that enables carbon dioxide turnover at limited cell voltages. During polarization tests, the tandem configuration demonstrated a photocurrent density of 0.2 mA/cm2 at a cell voltage of -2.6 V. That is 2-fold higher than the photocurrent density obtained with a solo photoanode (Cu||TiO2) and five orders of magnitude higher compared to the solo photocathode (Cu2O||Ni) design. Moreover, electrolysis under illumination (photoelectrolysis) showed a current density increase of 3.9 mA/cm2 with respect to electrolysis in the dark. However, this photocurrent density was merely apparent and was caused by light-triggered changes in the surface morphology and phase of Cu2O, which in turn affected the catalytic response. Moreover, the apparent partial ethylene photocurrent density and total partial current density during photoelectrolysis was 44 %, the highest among the detected products. That selectivity is attributed to the combined effect of Cu2O photoreduction and the associated local pH rise at the electrode-electrolyte interface.

Transition-Metal Porphyrin-Based MOFs In Situ-Derived Hybrid Catalysts for Electrocatalytic CO2 Reduction.

Excellent electrocatalytic CO2 reduction reaction activity has been demonstrated by transition metals and nitrogen-codoped carbon (M-N-C) catalysts, especially for transition-metal porphyrin (MTPP)-based catalysts. In this work, we propose to use one-step low-temperature pyrolysis of the isostructural MTPP-based metal-organic frameworks (MOFs) and electrochemical in situ reduction strategies to obtain a series of hybrid catalysts of Co nanoparticles (Co NPs) and MTPP, named Co NPs/MTPP (M = Fe, Co, and Ni). The in situ introduction of Co NPs can efficiently enhance the electrocatalytic ability of MTPP (M = Fe, Co, and Ni) to convert CO2 to CO, particularly for FeTPP. Co NPs/FeTPP endowed a high CO faradaic efficiency (FECOmax = 95.5%) in the H cell, and the FECO > 90.0% is in the broad potential range of -0.72 to -1.22 VRHE. In addition, the Co NPs/FeTPP achieved 145.4 mA cm-2 at a lower potential of -0.70 VRHE with an FECO of 94.7%, and the CO partial currents increased quickly to reach 202.2 mA cm-2 at -0.80 VRHE with an FECO of 91.6% in the flow cell. It is confirmed that Co NPs are necessary for hybrid catalysts to get superior electrocatalytic activity; Co NPs also can accelerate H2O dissociation and boost the proton supply capacity to hasten the proton-coupled electron-transfer process, effectively adjusting the adsorption strength of the reaction intermediates.

Synergizing Fe2O3 Nanoparticles on Single Atom Fe-N-C for Nitrate Reduction to Ammonia at Industrial Current Densities.

The electrochemical reduction of nitrates (NO3 -) enables a pathway for the carbon neutral synthesis of ammonia (NH3), via the nitrate reduction reaction (NO3RR), which has been demonstrated at high selectivity. However, to make NH3 synthesis cost-competitive with current technologies, high NH3 partial current densities (jNH3) must be achieved to reduce the levelized cost of NH3. Here, the high NO3RR activity of Fe-based materials is leveraged to synthesize a novel active particle-active support system with Fe2O3 nanoparticles supported on atomically dispersed Fe-N-C. The optimized 3×Fe2O3/Fe-N-C catalyst demonstrates an ultrahigh NO3RR activity, reaching a maximum jNH3 of 1.95 A cm-2 at a Faradaic efficiency (FE) for NH3 of 100% and an NH3 yield rate over 9 mmol hr-1 cm-2. Operando XANES and post-mortem XPS reveal the importance of a pre-reduction activation step, reducing the surface Fe2O3 (Fe3+) to highly active Fe0 sites, which are maintained during electrolysis. Durability studies demonstrate the robustness of both the Fe2O3 particles and Fe-Nx sites at highly cathodic potentials, maintaining a current of -1.3 A cm-2 over 24 hours. This work exhibits an effective and durable active particle-active support system enhancing the performance of the NO3RR, enabling industrially relevant current densities and near 100% selectivity.

Dynamic (Sub)surface-Oxygen Enables Highly Efficient Carbonyl-Coupling for Electrochemical Carbon Dioxide Reduction.

Nowadays, high-valent Cu species (i.e., Cuδ +) are clarified to enhance multi-carbon production in electrochemical CO2 reduction reaction (CO2RR). Nonetheless, the inconsistent average Cu valence states are reported to significantly govern the product profile of CO2RR, which may lead to misunderstanding of the enhanced mechanism for multi-carbon production and results in ambiguous roles of high-valent Cu species. Dynamic Cuδ + during CO2RR leads to erratic valence states and challenges of high-valent species determination. Herein, an alternative descriptor of (sub)surface oxygen, the (sub)surface-oxygenated degree (κ), is proposed to quantify the active high-valent Cu species on the (sub)surface, which regulates the multi-carbon production of CO2RR. The κ validates a strong correlation to the carbonyl (*CO) coupling efficiency and is the critical factor for the multi-carbon enhancement, in which an optimized Cu2O@Pd2.31 achieves the multi-carbon partial current density of ≈330 mA cm-2 with a faradaic efficiency of 83.5%. This work shows a promising way to unveil the role of high-valent species and further achieve carbon neutralization.

Permeability of Fusion-bonded epoxy coating to cathodic current: Pulsed current vs. direct current cathodic protection

This work aimed at investigating the permeability of Fusion-Bonded Epoxy (FBE) coating to cathodic current resulting from pulsed current cathodic protection (PCCP) in comparison to direct-current cathodic protection (DCCP). To accomplish this objective, a series of experimental techniques were employed, including chronoamperometry, chronopotentiometry, electrochemical impedance spectroscopy (EIS), and in-situ pH measurements. Subsequently, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and, X-ray photoelectron spectroscopy (XPS) analyses were conducted to examine the alterations in the chemistry of FBE. The FBE coating exhibits slight permeability to the cathodic current generated by the DCCP method, whereas it is relatively permeable and permeable to the cathodic current generated through the PCCP method at frequencies of 5 kHz and 10 kHz, respectively. Thus, the permeability of the FBE coating to the cathodic current was determined to be 7.23 %, 10.94 %, and 14.83 % after applying DCCP, PCCP-5 kHz, and PCCP-10 kHz, respectively. The use of the PCCP approach, as opposed to the DCCP method, results in more alterations to the FBE coating's chemistry. This new approach, in particular, leads to an increased absorption of water within the coating structure, which then enhances the formation of ion-conductive channels on the surface of the FBE coating. It is notable to state that, within the framework of the PCCP approach, the cathodic current permeability of the FBE coating exhibits enhancement as the frequency increases.

Local CO2 reservoir layer promotes rapid and selective electrochemical CO2 reduction

Electrochemical CO2 reduction reaction in aqueous electrolytes is a promising route to produce added-value chemicals and decrease carbon emissions. However, even in Gas-Diffusion Electrode devices, low aqueous CO2 solubility limits catalysis rate and selectivity. Here, we demonstrate that when assembled over a heterogeneous electrocatalyst, a film of nitrile-modified Metal-Organic Framework (MOF) acts as a remarkable CO2-solvation layer that increases its local concentration by ~27-fold compared to bulk electrolyte, reaching 0.82 M. When mounted on a Bi catalyst in a Gas Diffusion Electrode, the MOF drastically improves CO2-to-HCOOH conversion, reaching above 90% selectivity and partial HCOOH currents of 166 mA/cm2 (at −0.9 V vs RHE). The MOF also facilitates catalysis through stabilization of reaction intermediates, as identified by operando infrared spectroscopy and Density Functional Theory. Hence, the presented strategy provides new molecular means to enhance heterogeneous electrochemical CO2 reduction reaction, leading it closer to the requirements for practical implementation.

Constructing Zn-based MOF-MXene nanoarchitectures to stabilize ultrafine Pt nanocrystals with enhanced methanol oxidation performance

Although the development of direct methanol fuel cell technology is regarded as one rational option to against severe energy crises and environmental pollution, the low efficiency and considerable costs of current Pt-based anode catalysts largely impede the broad-scale commercialization. Herein, a convenient bottom-up approach is developed to the spatial construction of ultrafine Pt nanocrystals stabilized on a porous heterojunction matrix built from Zn-based metal organic frameworks and Ti3C2Tx MXene nanolamellas (Pt/ZIF-Ti3C2Tx) through the stepwise solvothermal reactions. The intercalation of metal organic frameworks produces plentiful cavities and channels for the dispersion and immobilization of small-sized Pt nanoparticles, while the incorporation of Ti3C2Tx nanosheets optimizes the Pt electronic structure and ensures a high electron conductivity. As a consequence, the as-acquired Pt/ZIF-Ti3C2Tx nanoarchitectures manifest exceptional electrocatalytic methanol oxidation abilities in terms of a large electrochemically active surface area of 110.5 m2 g−1, a high mass activity of 1900.1 mA mg−1, and preferable long-term stability, all of which are significantly superior to those of conventional Pt/carbon and Pt/unmodified Ti3C2Tx catalysts.

Modulating local environment for electrocatalytic CO2 reduction to alcohol

The fundamental drivers for the selective CO2 electroreduction reaction (CO2RR) to alcohol (e.g. C2H5OH) or alkene (e.g. C2H4) still remain unexplored. Previous studies mainly focus on catalyst engineering to enhance electrocatalytic performance, while the selectivity to alcohol has reached a bottleneck. Here, we modulate local environment to reveal the contribution of *CO and *H reaction intermediates in the selectivity of CO2 to alcohol/alkene on Cu electrocatalyst. Through modifications on local CO2 concentration, varied *CO/*H coverage ratios can be achieved. Based on the reaction kinetics analysis, we find that there is a direct connection between local CO2 concentration and interfacial *CO and *H coverage, which finally affects the selectivity of CO2 to alcohol or alkene. To verify this principle, polyvinylidene fluoride (PVDF), a hydrophobic binder, were selected and introduced into the catalyst surface for further enhancement of interfacial *CO/*H coverage. With PVDF decoration, alcohol/alkene ratio increased from 0.69 to 1.35. The Faradic Efficiency of alcohol is up to 37.5 % under a high current density of 800 mA cm–2 (a partial current density of 300 mA cm–2), surpassing most reported Cu-based materials. Our findings provide a fundamental guidance for CO2RR to alcohol under an industrial-level current density.

In-situ Zn-Al layered double hydroxide conversion coatings prepared on galvanized steels by a two-step electrochemical method

Zn-Al layered double hydroxide (LDH) pretreatment layer was prepared by a novel two-step electrochemical method on galvanized steel surface from a precursor solution containing Al3+-only. In the first step, anodic currents are applied to Zn deposit to produce Zn2+ in solution near the substrate surface. Cathodic currents are then applied to ensure the cathodic deposition of LDH film. The obtained LDH coatings not only provide excellent adhesion to the metal surface, but also enhance the adhesion between metal substrate and the top epoxy coatings. The “LDH/epoxy” painting system can protect galvanized steel from rusting for at least 150 days.