Bhavin Siritanaratkul

Bipolar membranes (BPM), composed of a cation exchange layer and an anion exchange layer, can enable steady-state operation at different pHs at the cathode and anode in electrolyzers. This enables the independent optimization of the cathode and anode catalysts for acidic and alkaline environments, respectively, which increases the scope for low-cost materials. Commercially available BPMs are operational only in a limited current range, therefore we aimed to develop custom BPMs for higher currents that are easily fabricated, mechanically stable, and suitable for storage in dry form. We used commercial single membranes combined with TiO ₂ as the water dissociation catalyst in the junction, and have developed a hot-pressing method to prepare self-standing membranes that are mechanically robust, without a loss in electrochemical performance. Electrochemical Impedance Spectroscopy (EIS) was used to deconvolute the water dissociation resistance from other processes, leading to better understanding of the parameters that determine BPM performance. We demonstrate that the higher-performance BPMs surpass commercial BPMs for use in water electrolyzers, primarily due to a large decrease in the water dissociation overpotential to < 400 mV at 0.5 A cm ^-2 at 60 °C compared to ~1.3 V for the benchmark material. We also show how the membranes can be employed for high current density CO ₂ electrolysis in a device structure that enable high CO ₂ utilization efficiency, with the hot-pressed membranes achieving lower cell voltage and higher CO Faradaic efficiency compared to our previous reports with a custom BPM.

‘Through-electrode’ vibrational sum frequency generation elucidates the interface structure of CH ₃ CN in the electric double layer. Changes to micro-environments are observed in the presence of H ₂ O and N -methyl-2-pyrrolidone additives.

We report herein the synthesis, spectroscopic and electrochemical characterization, as well as electrocatalytic properties toward heterogeneous electrochemical CO₂ reduction of two mononuclear copper(II) complexes, namely, [Cu(L)]²⁺ (1) and [Cu(QTPy)]²⁺ (2), where L = 8-([2,2'-bipyridin]-6-yl)-2-(pyridin-2-yl)quinoline and QTPy = 2,2':6',2″:6″,2‴-quaterpyridine. The two complexes 1 and 2 have been first successfully immobilized onto multiwalled carbon nanotubes (MWCNTs) grafted on glassy carbon electrodes, as shown by X-ray photoelectron spectroscopy and cyclic voltammetry. Electroreduction of carbon dioxide by the grafted complexes has been investigated in an aqueous KHCO₃ medium at neutral pH. Comparative studies highlight the better catalytic performance of the complex bearing L rather than QTPy under the same experimental conditions. Controlled potential electrolysis (CPE) at low overpotential (-0.55 V vs reversible hydrogen electrode (RHE)) displays high selectivity for carbon monoxide production with complex 1 (Faradaic efficiency (FE_CO = 75%)). Furthermore, in situ and ex-situ analyses of the electrolysis evidence no modification of the immobilized mononuclear complex upon CPE, which is rare for grafted copper systems as well as no leach of copper in the electrolyte solution. Noteworthy, the implementation of the complexes into zero-gap electrolyzers allows the strong enhancement of FE_CO for complex 1, reaching 100% at -0.60 V vs RHE, whereas complex 2 remains poorly selective, hence clearly highlighting the strong impact of the ligand topology on the catalytic properties of the complexes.

We report herein the synthesis, spectroscopic and electrochemical characterization as well as electrocatalytic properties toward heterogeneous electrochemical CO2 reduction of two mononuclear copper(II) complexes, namely [Cu(L)]2+ (1) and [Cu(QTPy)]2+ (2) where L = 8-([2,2'-bipyridin]-6-yl)-2-(pyridin-2-yl)quinoline and QTPy = 2,2':6',2'':6'',2'''-quaterpyridine. The two complexes 1 and 2 have been first successfully immobilized onto multiwalled carbon nanotubes (MWCNTs) glassy carbon electrodes as shown by X-ray photoelectron spectroscopy and cyclic voltammetry. Electroreduction of carbon dioxide by the grafted complexes has been investigated in aqueous KHCO3 medium at neutral pH. Comparative studies highlight the better catalytic performance of the complex bearing L rather than QTPy under the same experimental conditions. Controlled potential electrolysis (CPE) at low overpotential (–0.55 V vs RHE) displays high selectivity for carbon monoxide production with complex 1 (Faradaic Efficiency (FECO = 75%)). Furthermore, in-situ and ex-situ analyses of the electrolysis evidence no modification of the immobilized mononuclear complex upon CPE which is rare for grafted copper systems, as well as no leach of copper in the electrolyte solution. Noteworthy, implementation of the complexes into zero-gap electrolysers allows the strong enhancement of FECO for complex 1, reaching 100% at –0.60 V vs RHE, whereas complex 2 remains poorly selective, hence clearly highlighting the strong impact of the ligand topology on the catalytic properties of the complexes.

Bipolar membranes (BPM), composed of a cation exchange layer and an anion exchange layer, can enable steady-state operation at different pHs at the cathode and anode in a water electrolyzer. This allows optimizing the cathode and anode catalysts for acidic and alkaline environments, respectively, which increases the scope for low-cost materials. Commercially available BPMs are operational only in a limited current range, therefore we aimed to develop custom BPMs for higher currents that are easily fabricated, mechanically stable, and suitable for storage in dry form. We used commercial single membranes combined with TiO2 as the water dissociation catalyst in the junction, and found that spin-coating of TiO2 yielded reproduceable interfaces for water dissociation. Electrochemical Impedance Spectroscopy (EIS) was used to deconvolute the water dissociation resistance from other processes, leading to better understanding of the parameters that determine BPM performance. Hot-pressing of the BPM led to stronger adhesion of the two membrane layers, creating a durable self-standing BPM. Using this workflow, future high-performance BPMs can be developed and investigated, for use not only in water electrolyzers but also CO2 electrolyzers where BPMs are required for higher CO2 utilization efficiency.

Copper nanowires with fivefold twinned structures (t-CuNWs) are shown to be effective as cathode catalysts for the electrochemical reduction of CO₂ (CO₂RR) in a zero-gap electrolyzer to produce ethylene.

This study investigates copper nanowires with fivefold twinned structures (t-CuNWs) as catalysts for the electrochemical reduction of CO2 (CO2RR) in a zero-gap flow cell with 1 M KOH as anolyte. The t-CuNWs, with surfaces enclosed by (100) facets, were selected for their enhanced CO adsorption strength, which promotes C–C coupling—a key pathway toward multi-carbon (C2+) products. Additionally, the entangled t-CuNWs exhibits enhanced hydrophobicity when compared to commercial Cu nanoparticles (CuNPs), which can reduce flooding issues and contribute to high stability during electrochemical operation. These characteristics distinguish t-CuNWs from CuNPs in terms of activity and stability. The t-CuNWs exhibited ~ 40% C2H4 faradic efficiency (FE) for more than 4 hours under a current density of 100 mA/cm2, while commercial CuNPs exhibited ~ 20% C2H4 FE for less than 4 hours under the same condition. These findings highlight the potential of (100) faceted t-CuNWs for efficient and durable C2+ product formation in CO2RR with facet engineering and hydrophobicity control.

The electrochemical reduction of CO ₂ is a promising pathway for converting CO ₂ into valuable fuels and chemicals. The local environment at the cathode of CO ₂ electrolyzers plays a key role in determining activity and selectivity, but currently some mechanisms are still under debate. In particular, alkali metal cations have been shown to enhance the selectivity of metal catalysts, but their role remains less explored for molecular catalysts especially in high-current electrolyzers. Here, we investigated the enhancement effects of cations (Na ⁺ , K ⁺ , Cs ⁺ ) on Co phthalocyanine (CoPc) in a state-of-the-art reverse-biased bipolar membrane electrolyzer. When added to the anolyte, these cations increased the Faradaic efficiency for CO, except in the case of Na ⁺ in which the effect was transient, but the effects are convoluted with the transport process through the membrane. Alternatively, these cations can also be added directly to the cathode as chloride salts, allowing the use of a pure H ₂ O anolyte feed, leading to sustained improved CO selectivity (61% at 100 mA cm ⁻² after 24 h). Our results show that cation addition is a simple yet effective strategy for improving the product selectivity of molecular electrocatalysts, opening up new avenues for tuning their local environment for CO ₂ reduction. This article is part of the discussion meeting issue ‘Green carbon for the chemical industry of the future’.

An emerging concept and platform, the electrochemical Leaf (e-Leaf), offers a radical change in the way tandem (multi-step) catalysis by enzyme cascades is studied and exploited. The various enzymes are loaded into an electronically conducting porous material composed of metallic oxide nanoparticles, where they achieve high concentration and crowding – in the latter respect the environment resembles that found in living cells. By exploiting efficient electron tunneling between the nanoparticles and one of the enzymes, the e-Leaf enables the user to interact directly with complex networks, rendering simultaneous the abilities to energise, control and observe catalysis. Because dispersion of intermediates is physically suppressed, the output of the cascade – the rate of flow of chemical steps and information – is delivered in real time as electrical current. Myriad enzymes of all major classes now become effectively electroactive in a technology that offers scalability between micro-(analytical, multiplex) and macro-(synthesis) levels. This Perspective describes how the e-Leaf was discovered, the steps in its development so far, and the outlook for future research and applications.