A Flowing Electrolyte Interlayer (FEI) electrolyzer is demonstrated for CO 2 reduction. The 3-layer cell includes an anion-exchange membrane, a cation-exchange membrane, and a flowing interlayer that serves as a product-collection stream. The new cell was evaluated using copper-based electrocatalysts, including CuSn 0.03 , CuSn 4 , and Cu 2 Se, for the selective production of ethanol and direct recovery of free acid (formic acid or acetic acid). Analyses, including operando ED-XRD and XAS, confirm structural stability of cell components. The FEI electrolyzer retained up to 63% ethanol Faradaic efficiency while enabling direct recovery of liquid products and suppressing anode crossover to below 2%, a more than 40-fold reduction compared with conventional MEA systems. Channel geometry and flow experiments revealed that product removal is limited at relatively low flow velocities and may be diluted at higher velocities. An optimal interlayer channel configuration was shown to deliver up to 9 weight percent ethanol for over 60 h.

Taking advantage of the potentially low-cost and environmentally friendly nature of renewable energy sources like wind and photovoltaics has long been the aim of the CO2 electrolysis field. However, there have been sparse reports on the economic and performance implications of coupling these two systems. In this perspective, we present lessons that can be taken from work done in water electrolysis, summarize the progress that has been made in coupling electrochemical CO2 reduction systems to intermittent renewable energy sources, and perform a brief economic analysis on energy versus product storage in intermittent systems. Finally, we recommend future research directions, including rigorous studies on the effects of dynamic operation on electrolyzer components, strategies for integrating with continuous downstream processes, synergistic post-product processing via electrification technologies, and leveraging of artificial intelligence and automation to mitigate the unpredictability of CO2 electrolysis.

We investigate the reduction of CO2 to ethylene across buffered anolyte pH values 4 to 14 using a copper-phosphorus (Cu-P) electrocatalyst in a zero-gap membrane electrode assembly. Electrochemical CO2 reduction using alkaline electrolytes typically shows limited carbon efficiencies and single-pass efficiencies, while acidic conditions typically favor the hydrogen evolution reaction. Results from this work show that weakly phosphate-buffered acidic anolytes (pH 6) maximize ethylene production with a 73% FE at 300 mA cm-2 and 51% FE at 500 mA cm-2, including a 51% single-pass CO2 conversion efficiency for over 400 h of continuous operation. We propose a mechanism based on pH-dependent CO coverage that controls the selectivity at the *HCCOH intermediate. Low CO coverage at pH 6 favors hydroxide elimination to *CCH, yielding ethylene (98% of C2 products), while high coverage at pH 14 promotes hydrogenation to ethanol (44% of C2). The HER mechanism transitions from H2O-mediated at pH 14 to phosphate-mediated (H2PO4 -/HPO4 2-) at weakly acidic pH, minimizing HER competition at pH 6. This mechanistic understanding enables controlled C2 product selectivity through manipulation of the CO coverage and local proton activity.

Electrolytic CO reduction was investigated at copper electrocatalysts in zero-gap membrane electrode assemblies as a function of buffering agents and cofeeding with CO2 or Ar. Results show an acetate Faradaic efficiency (FE) of 90% at 300 mA cm-2 using pure CO feeds and phosphate-buffered anolyte near pH 8. When using CO feeds with more alkaline anolytes, the hydrogen evolution reaction becomes the dominant reduction reaction, independent of the buffer. Product distributions of cofeeding experiments with CO and CO2 show that increasing CO2 cofeeding results in increased selectivity toward ethylene (42% FE) in near-neutral KHCO3 anolytes or ethanol (40% FE) in alkaline KOH anolytes. Evaluation of several commercial anion exchange membranes shows similar selectivity trends, suggesting product selectivity is dominated by the local pH and surface coverage of CO. Based on these results, we propose pH buffering and CO coverage behaviors that facilitate high selectivities to acetate.

Recent Die-to-Die (D2D) interconnects require high data rates operating at high frequencies (> 10 GHz) in multichip packages. Mechanical adhesion was utilized to improve the reliability of traditional packages by increasing interface roughness between epoxy dielectrics and electrochemically deposited copper interconnects. The classical packages, operating at low frequencies below 1 GHz, showed a negligible scattering of electromagnetic waves (S21 < 0.5 dB/m) on the rough surface [1, 2]; however, recent interconnects present considerable degradation in power losses (S21 > 1.0 dB/m) on the rough surface due to skin effect at high frequencies (> 10 GHz) [2]. While previous works have shown the impact of surface roughness on adhesion enhancement, a trade-off between adhesion and power losses has not been precisely considered. This study investigates the trade-off between reliability and performance. We explore the impact of surface roughness on adhesion and power efficiency of electrochemically deposited copper interconnects at high frequencies up to 18 GHz. Wet etching was performed to modify surface roughness for low-cost production. The root-mean-square roughness (RRMS) is regulated at ~10-100 nm to examine smooth copper-epoxy interfaces for future D2D interconnects. The surface morphology is analyzed by atomic force microscopy (AFM). Adhesion and insertion losses are investigated by peel test and vector network analyzer. A direction for future work is provided to improve chemical adhesion at a smooth copper-epoxy interface. Chemical adhesion is expected to improve the reliability of future multichip packages while maintaining power integrity. For example, surface oxidation and silane coupling agents are discussed to improve chemical adhesion at the smooth interface (< 100 nm RRMS). REFERENCES: [1] Lau, J.H., Recent Advances and Trends in Advanced Packaging. IEEE Transactions on Components, Packaging and Manufacturing Technology, 2022. 12(2): p. 228-252. [2] Gold, G. and K. Helmreich, A physical surface roughness model and its applications. IEEE Transactions on Microwave Theory and Techniques, 2017. 65(10): p. 3720-3732.

The electrochemical reduction of CO2 to C2 products is believed to proceed via the formation of adsorbed CO as an intermediate. Although ethylene is frequently reported as the main product when using Cu electrocatalysts, recent studies have demonstrated that directly feeding CO can result in the selective formation of acetate. In this study, we investigate the electrochemical reduction of CO2 and CO using Cu electrocatalysts prepared by a one-pot synthesis method employing hydrazine as a reducing agent and polyvinylpyrrolidone (PVP) as a capping agent in a Membrane Electrode Assembly (MEA) cell configuration. We investigated the electrochemical reduction of CO2 and CO using Cu electrocatalysts prepared by a one-pot synthesis method in a Membrane Electrode Assembly (MEA) cell configuration. While CO2 reduction primarily yields ethylene (36.99%), followed by hydrogen, CO, and ethanol, feeding CO directly under the same potential increases the total C2 product yield from 52% to 83%, with acetate becoming the dominant product at 63%. Employing a phosphate buffer to maintain an alkaline pH of 8 further enhances acetate selectivity, reaching 90% with KOH. We propose a mechanism involving a common acetyl intermediate for ethylene formation from CO2 and a ketene intermediate for CO reduction to acetate. Our results highlight the significant impact of feed, electrolyte composition, and pH on product distribution, with direct CO reduction favoring C2 products and alkaline pH promoting acetate selectivity. These findings offer insights for optimizing the electrochemical reduction of CO2 and CO. Figure 1

Future multichip packages require Die-to-Die (D2D) interconnects operating at frequencies above 10 GHz; however, the extension of copper interconnects and epoxy dielectrics presents a trade-off between performance and reliability. This paper explores insertion losses and adhesion as a function of interface roughness at frequencies up to 18 GHz. We probe epoxy surface chemistry as a function of curing time and use wet etching to modulate surface roughness. The morphology is quantified by atomic force microscopy (AFM) and two-dimensional fast Fourier transform (2D FFT). Peel test and vector network analysis are used to examine the impacts of both type and level of roughness. The trade-offs between power efficiency and reliability are presented and discussed.

Ethylene is typically reported as the primary product from CO 2 reduction at copper electrocatalysts in MEA-type cell configurations with alkaline anolytes. In this work, we evaluate CO 2 reduction selectivity at Cu-P, Cu-Sn, and Cu 2 Se electrocatalysts that were synthesized via a common one-pot approach. Electron microscopy, X-ray diffraction and inductively coupled plasma optical emission spectrometry show 100-110 nm nanoparticles with uniform distributions of P, Sn, or Se. When using neutral (0.1 M KHCO 3 ) anolytes, electrocatalysts with P-doping yield increases in ethylene Faradaic efficiency (up to 52 % at 150 mA cm -2 ) while Cu-Sn and Cu-Se electrocatalysts result in increased oxygenate selectivity. Cu-Sn electrocatalysts yield an FE of 24 % ethanol at 150 mAcm -2 and Cu 2 Se electrocatalysts yield an FE of 32 % to acetate at 150 mAcm -2 . More alkaline anolytes (1 M KOH) further increased oxygenate formation, with 48 % ethanol Faradaic efficiency on Cu-Sn and 40 % acetate Faradaic efficiency on Cu 2 Se at 350 mA cm -2 . Galvanostatic experiments were conducted at 150 mA cm -2 in 0.1 M KHCO 3 electrolyte for over 200 h for the three electrocatalysts. Figure 1 shows the slow losses in FEs to C 2 products (0.02 % per h) and increasing cell potentials (1 mV per h). In this talk, we consider the mechanisms for selectivity and the nature of durability improvements. Figure 1

Future processes and materials are needed to enable multichip packages with chip-to-chip (C2C) data rates of 50 GB/s or higher. This presents a fundamental challenge because of the skin effect, which exacerbates signal transmission losses at high frequencies. Our results indicate that smooth copper interconnects with relatively thin cuprous oxides (Cu2O, CuI) and amine-functional silane adhesion promoters improve interfacial adhesion with epoxy dielectrics by nearly an order of magnitude. For the first time, we present X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy evidence of Cu(I)-O-Si bond formation at silane-treated interfaces. Thus, relatively smooth interconnects can benefit from reduced skin losses while maintaining their mechanical integrity and reliability. Failure mechanisms of Cu interconnects with cuprous and cupric oxide (CuO, CuII) are explored using scanning electron microscopy (SEM) and Auger electron spectroscopy (AES). These results indicate that both cupric oxides and relatively thick cuprous oxide interfaces lead to relatively weaker interfaces compared with thin cuprous oxides with adhesion promoters.

Ethylene is well known as the primary product of CO 2 reduction at Cu electrocatalysts using zero-gap membrane electrode assembly cells with gas diffusion cathodes. Other types of Cu electrocatalysts including oxide-derived Cu, CuSn and CuSe yield relatively more C 2 oxygenates; however, the mechanisms for C 2 product selectivity are not well established. This work considers selectivity trends of Cu-P 0.065 , Cu-Sn 0.03 , and Cu 2 Se electrocatalysts made using a standard one pot synthesis method. Results show that Cu-P 0.065 electrocatalysts (Cu δ + = 0.13) retain ethylene as a primary product with relatively higher Faradaic efficiencies (FE = 43% at 350 mA cm −2 ) than undoped Cu electrocatalysts (FE = 31% at 350 mA cm −2 ) at the same current density. The primary CO 2 reduction product at Cu-Sn 0.03 (Cu δ + = 0.27) electrocatalysts shifts to ethanol (FE = 48% at 350 mA cm −2 ) while CO 2 reduction at Cu 2 Se (Cu δ + = 0.47) electrocatalysts favor acetate production (FE = 40% at 350 mA cm −2 ). Based on these results, we propose a common acetyl intermediate and a mechanism for selective formation of ethylene, ethanol or acetate based on the degree of partial positive charge ( δ + ) of Cu reaction sites.

We explore the impact of pH and buffer on the electrochemical reduction of CO at Cu electrocatalysts in a membrane electrode assembly (MEA) cell. Anolytes included alkaline KOH solution with potassium hydrogen phosphate and potassium dihydrogen phosphate buffers with pH values ranging from 8 to 14. Results show near-neutral pH electrolytes enhance acetate selectivity. Figure 1 shows Faradaic efficiencies to acetate over 85% at a current density of 300 mA/cm². More alkaline electrolytes resulted in increasing HER along with coproduction of ethanol and n-propanol. Previous works have shown that ethylene production is enhanced at near-neutral pH values and other works have demonstrated that acetate is more favored in alkaline conditions, with ketene identified as a key intermediate. This study highlights the role of phosphate buffers in acetate selectivity at near-neutral pH. SEM, XPS, and XRD analyses show morphological and compositional changes in the Cu catalyst under different pH conditions. We propose that the phosphate buffers stabilize acetate precursors. Figure 1: Electrochemical performance measurement at different anolyte pH; Faradaic Efficiency of H 2 , C 2 H 4 , CH 4 , Ethanol, Acetate, and n-Propanol during CO electroreduction in a zero-gap MEA configuration at 300 mA*cm −2 . Figure 1

In this study Cu, Sn, and bimetallic CuSnx nanoparticles were synthesized and evaluated as electrocatalysts for CO2 reduction using zero gap membrane electrode assemblies. Results show bimetallic electrocatalysts with Sn contents above 10% yield formate as a primary product with Faradaic Efficiencies near 70% at 350 mA cm(-2). Cu-Sn-x electrocatalysts with less than 10% Sn yield CO at current densities below 350 mA cm(-2) and relatively lower cell potentials. When the low-Sn content bimetallic electrocatalysts were evaluated in alkaline anolytes at 350 mA cm(-2), ethanol was recorded as the primary product (FE = 48.5% at E-cell >= 3.0 V). We propose enhanced C-2 activity and selectivity originate from Cu dimers adjacent to Sn atoms for bimetallic electrocatalyst with low-Sn content. The C-2 active sites are lost when the surface Sn content exceeds 25%-38%.

Electrochemical reduction of CO2 in membrane electrode assembly (MEA) cells with gas diffusion electrodes (GDEs) offers a sustainable path to produce chemicals and fuels. Although these systems enable high-current densities and Cu electrocatalysts favor C2+ products like ethylene, the mechanisms controlling selectivity towards specific C2 products (ethylene, ethanol, and acetate) are not well understood. This study explores CO2 reduction selectivity trends and mechanisms on Cu-based electrocatalysts, emphasizing multicarbon product formation using different Cu alloys. In particular, CuSnx, Cu-P, and Cu-Se electrocatalysts were synthesized via a one-pot method and tested in MEA cells with alkaline electrolytes. Several ex situ characterization techniques (XRD, XPS, SEM, EDS, and ICP-OES) were employed to study the structural, compositional, and electronic properties of the electrocatalysts. Sn content in CuSnx alloys critically influenced the main CO2 reduction product, with high Sn (x ≥ 0.10) promoting formate. and low Sn (x ≤ 0.10) favoring CO, ethylene, and ethanol, depending on cell potential and pH. Comparing Cu, Cu-P0.065, Cu-Sn0.03, and Cu2Se electrocatalysts revealed the impact of dopants, alloys, and compounds on selectivity. In 0.1 M KHCO3, P-doped Cu showed higher ethylene FE (52%) than pure Cu (31%), while Cu-Sn and Cu-Se favored ethanol (24% FE) and acetate (32% FE), respectively. In 1 M KOH, Sn alloys promoted ethanol (48% FE), and Cu-Se achieved high acetate selectivity (40% FE) at 350 mA cm-2. The electrocatalysts demonstrated stability over 250 hours. A mechanism involving a common acetyl intermediate is proposed, with selectivity governed by the partial positive charge (δ+) on Cu sites calculated using density functional theory (DFT). Cu-P0.065 (Cuδ+ = 0.13) promotes ethylene, Cu-Sn0.03 (Cuδ+ = 0.27) favors ethanol, and Cu2Se (Cuδ+ = 0.47) enhances acetate selectivity.

Carbon dioxide electrolyzers capable of maintaining stable performance for thousands of hours are necessary for commercial electrochemical reduction of CO 2 to two-carbon products such as ethanol and ethylene. Currently, most studies containing CO 2 reduction to two-carbon products have been for durations of under 20h. Only a few (<5) instances of CO 2 reduction to two-carbon products at durations over 100h have been reported. Common cell failure mechanisms, such as carbonate salt precipitation and cathode flooding, can be mitigated by tuning the operating conditions of the reactor. Beyond these modes of failure, there are practical limitations related to materials' durabilities and long-term stabilities, including ionomeric membranes' operating lifetimes, gas diffusion cathodes, anodes, and other MEA components. In this presentation, we explore the role of CO 2 , water, and ion transport on cell performance over extended periods of operation. The polymeric anion exchange membrane and conductive binder have been identified as crucial components in tuning the transport properties of electrolyzer systems and, thus, will be the focus of this study. We consider several types of anion exchange membranes (e.g., imidazolium, ammonium, piperindinium) and conductive binders (e.g., Nafion, PVDF, PTFE, PSMIM) for use in the direct reduction of CO 2 to two-carbon products at nanoscale Cu electrodes (150mA/cm 2 , 0.01M KHCO 3 anolyte). This work improves upon previous analysis of membrane and binder transport properties by testing a wider variety of materials for >100h durations and reporting specific cell failure times and causes. We will discuss the balances between carbonate precipitation, flooding, and other membrane or electrode failures as a function of materials, MEA preparation, and operating conditions. A comprehensive set of failure standards based on electrolyzer performance (pressure, outlet mass flow, two-carbon product Faradaic efficiencies, energy efficiency, carbon efficiency) is introduced, and electrolyzer configurations are tested in triplicate to produce statistically significant failure data. Overall, this provides insight into CO 2 , ion, and water transport's role in electrolyzer cell performance and failure mechanisms. Figure 1

Recent works have shown that the electrochemical reduction of CO2 or CO to C2 products may be carried out at high rates and selectivities using electrolyzers with copper catalysts, gas diffusion electrodes (GDEs), and anion exchange membranes (AEMs). The current densities and Faradaic efficiencies reported for CO2 reduction are similar to those used in the commercial production of chlorine via the Chlor-alkali process; however, other performance metrics related to the energetic efficiency, carbon efficiency, single-pass conversion, crossover, and durability or operating lifetime are also important considerations. Work in our labs indicates that operating lifetimes are typically related to flooding, precipitation, or catalyst deactivation. As shown in Figure 1a, flooding in CO2 electrolyzers is typically observed with a sharp increase in hydrogen production and increased cathode gas flows. Figure 1b shows evidence of carbonate precipitation including variations in cell potential and lower cathode flow. In this talk, we consider the relationships between AEM properties (conductivity, water transport, counter ion transport), binder properties (viz. hydrophobicity), and catalysts on operating lifetimes of CO2 electrolyzers. Figure 1

Conventional hydrogen separations from reformedhydrocarbons often deploy a water gas shift (WGS) reactor to convertCO to CO2, followed by adsorption processes to achieve pure hydrogen.The purified hydrogen is then fed to a compressor to deliver hydrogenat high pressures. Electrochemical hydrogen pumps (EHPs) featuringproton-selective polymer electrolyte membranes (PEMs) represent analternative separation platform with fewer unit operations because theycan simultaneously separate and compress hydrogen continuously. Inthis work, a high-temperature PEM (HT-PEM) EHP purified hydrogento 99.3%, with greater than 85% hydrogen recovery for feed mixturescontaining 25-40% CO. The ion-pair HT-PEM and phosphonic acidionomer binder enabled the EHP to be operated in the temperaturerange from 160 to 220 degrees C. The ability to operate the EHP at an elevated temperature allowed the EHP to purify hydrogenfrom gas feeds with large CO contents at 1 A cm-2. Finally, the EHP with the said materials displayed a small performance lossof 12 mu Vh-1for purifying hydrogen from syngas for 100 h at 200 degrees C.

A cellulose nanofiber (CNF)–polyacrylamide (PAM) hydrogel electrolyte is developed. It has the potential to expand the application of ZIBs to broad fields such as wind turbines in desolate areas, cold polar regions, and aerospace.

High-entropy alloys (HEAs) have intriguing material properties, but their potential as catalysts has not been widely explored. Based on a concise theoretical model, we predict that the surface of a quaternary HEA of base metals, CoCrFeNi, should go from being nearly fully oxidized except for pure Ni sites when exposed to O2 to being partially oxidized in an acidic solution under cathodic bias, and that such a partially oxidized surface should be more active for the electrochemical hydrogen evolution reaction (HER) in acidic solutions than all the component metals. These predictions are confirmed by electrochemical and surface science experiments: the Ni in the HEA is found to be most resistant to oxidation, and when deployed in 0.5 M H2SO4, the HEA exhibits an overpotential of only 60 mV relative to Pt for the HER at a current density of 1 mA/cm2.

Secondary lithium-bromine (Li-Br-2) batteries offer cell potentials near 4 V and storage capacities over 1200 Whkg(-1)-LiBr. Here, we demonstrate Li-Br-2 cells with two types of carbonized metal-organic frameworks (MOFs). Carbonized MIL-53(Al) electrodes show capacities of 224 mAhg(-1) LiBr (at 3.4 V) and 72% capacity retention after 100 cycles, while carbonized ZIF-8 electrodes show specific capacities of 273 mAhg(-1) LiBr and 88% capacity retention over 100 cycles at 1C (at 3.4 V). Surface characterization (XPS, EDS) and porosimetry indicate that the ZIF-8 derived MOF electrodes are heavily microporous with heteroatom (C-N) doping. The increased capacity and reversibility of ZIF-8 derived carbon during cyclic voltammetry and cycling measurements is ascribed to higher LiBr loadings, enhanced bromine trapping and adsorption due to the electrode microporosity and heteroatom bonding.

The presence of surface/deep defects in 4d- and 5d-perovskite oxide (ABO(3), B = Nb, Ta, Mo, etc.) nanoparticles (NPs), originating from multivalent B-site cations, contributes to suppressing their metallic properties. These defect states can be removed using a H-2/Ar thermal treatment, enabling the recovery of their electronic properties (i.e., low electrical resistivity, high carrier concentration, etc.) as expected from their electronic structure. Therefore, to engineer the electronic properties of these metastable perovskites, an oxygen-controlled crystallization approach coupled with a subsequent H-2/Ar treatment was utilized. A comprehensive study of the effect of the post-treatment time on the electronic properties of these perovskite NPs was performed using a combination of scattering, spectroscopic, and computational techniques. These measurements revealed that a metallic-like state is stabilized in these oxygen-reduced NPs due to the suppression of deep rather than surface defects. Ultimately, this synthetic approach can be employed to synthesize ABO(3) perovskite NPs with tunable electronic properties for application into electrochemical devices.