The pH at the electrocatalyst surface plays a key role in defining the activity and selectivity of the CO 2 reduction reaction (CO 2 RR). We report here operando Raman measurements of the catalyst surface in a customized CO 2 RR flow cell that enable the measure of pH. Using this flow cell, we were able to measure surface pH as a function of time, current density, and proximity to the catalyst surface during the electrolysis of bicarbonate solutions. We observed that increasing the current density from 0 to 200 mA cm −2 increased the surface pH from 8.5 to 10.3. We also show here that operation at elevated temperatures (70 °C) results in an increased surface pH and serves to suppress the competing and undesirable hydrogen evolution reaction.

Gas-fed CO2 electrochemical flow reactors are appealing platforms for the electrolytic conversion of CO2 into fuels and chemical feedstocks at commercially relevant current densities (≥100 mA/cm2). An inherent challenge in the development of these reactors is delivering sufficient water to the cathode to sustain the CO2 reduction reaction, while also preventing accumulation of excess water at the porous cathode (i.e., flooding). We present herein experimental evidence showing cathode flooding in a zero-gap electrolyzer at 200 mA/cm2. This flooding causes a 37% decrease in partial current density for CO production (j CO) along with a 450 mV increase in cell voltage (E cell). We show that the detrimental effects associated with this flooding can be mitigated by pairing thin membranes (i.e., ≤40 μm) with hydrophobic cathodes to enable CO2 electrolysis at commercially relevant conditions (j CO ≥ 100 mA/cm2 and E cell < 3 V).

Lattice strain can enhance the activity and selectivity of electrochemical reactions by breaking the linear scaling relationship. Notwithstanding, the explicit use of strain to affect the CO2 reduction reaction (CO2RR) is rarely reported. In this Perspective, we highlight the opportunity to use strain to affect the activity and selectivity of CO2RR electrocatalysts. We summarize the existing challenges in isolating the influence of strain from convoluting factors (e.g., size, shape, electronic, and surfactant effects) that result from typical methods of inducing strain. We also propose ways to isolate strain effects using the application of mechanical strain to thin-film CO2RR catalysts. We designed this Perspective to motivate  the use of joint empirical and computational studies to investigate CO2RR strain–activity–selectivity relationships.

Electrocatalytic palladium membrane reactors (ePMRs) use electricity and water to drive hydrogenation reactions without forming H2 gas.

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Strain engineering can increase the activity and selectivity of an electrocatalyst. Tensile strain is knownt o improve the electrocatalytic activity of palladium electrodes for reduction of carbon dioxide or dioxygen, but determining how strain affects the hydrogen evolution reaction (HER) is complicated by the fact that palladium absorbs hydrogen concurrently with HER. We report here ac ustom electrochemical cell, whichapplies tensile strain to aflexible working electrode,t hat enabled us to resolve howt ensile strain affects hydrogen absorption and HER activity for at hin film palladium electrocatalyst. When the electrodes were subjected to mechanically-applied tensile strain, the amount of hydrogen that absorbed into the palladium decreased, and HER electrocatalytic activity increased. This study showcases how strain can be used to modulate the hydrogen absorption capacity and HER activity of palladium.

We report here an electrochemical flow reactor that converts limestone (CaCO3(s)) into Ca(OH)2(s) at a high production rate and co-produces pure CO2(g).

Here, we quantify the effect of an external magnetic field (β) on the oxygen evolution reaction (OER) for a cobalt oxide|fluorine-doped tin oxide coated glass (CoO x |FTO) anode. A bespoke apparatus enables us to precisely determine the relationship between magnetic flux density (β) and OER activity at the surface of a CoO x |FTO anode. The apparatus includes a strong NdFeB magnet (β max = 450 ± 1 mT) capable of producing a magnetic field of 371 ± 1 mT at the surface of the anode. The distance between the magnet and the anode surface is controlled by a linear actuator, enabling submillimeter distance positioning of the magnet relative to the anode surface. We couple this apparatus with a finite element analysis magnetic model that was validated by Hall probe measurements to determine the value of β at the anode surface. At the largest tested magnetic field strength of β = 371 ± 1 mT, a 4.7% increase in current at 1.5 V vs the normal hydrogen electrode (NHE) and a change in the Tafel slope of 14.5 mV/dec were observed. We demonstrate through a series of OER measurements at sequential values of β that the enhancement consists of two distinct regions. The possible use of this effect to improve the energy efficiency of commercial water electrolyzers is discussed, and major challenges pertaining to the accurate measurement of the phenomenon are demonstrated.