Tuning the RWGS Reaction via EPOC and In Situ Electro-oxidation of Cobalt Nanoparticles

Abstract

The electrochemical promotion of catalytic activity by non-noble transition metals is rarely reported in the literature. Here, Co nanoparticles were utilized for the electrochemical activation of CO2 hydrogenation under atmospheric pressure conditions. A range of transient kinetic experiments in conjunction with X-ray photoelectron spectroscopy and imaging techniques were employed to correlate the observed catalytic activity with the electronic and morphological characteristics of the cobalt catalyst surface. Our results show that migrating ions from the solid electrolyte to the catalyst surface has a dual effect, which has an impact on the observed catalytic behavior. First, they lead to an electrochemically formed double layer on the catalyst surface, which effectively modifies the catalyst work function and consequently alters the observed catalytic rate. Second, they have a profound effect on the oxidation state of cobalt and therefore on the structure of the cobalt oxide particles formed. The presence of Co oxide phases upon anodic polarization shows up to a 5-fold increase in the catalytic rate of the reverse water gas shift (RWGS) reaction. The enhancement of the catalytic activity observed in this work, with a relatively inexpensive cobalt oxide film, is comparable to that obtained with noble metal catalysts in classical EPOC studies. The present study also demonstrates that the formation of different oxide phases can be controlled accurately by electrochemical means and used to tune the catalytic activity and selectivity of cobalt. The reported results could guide the design and operation of more selective and active catalytic processes for the RWGS reaction.

Electrochemical promotion of copper nanoparticles for the reverse water gas shift reaction

“…53 The catalyst was activated above 300 °C and the catalytic rate increased with temperature in all cases. Under the same conditions, the open-circuit CO rate showed to be two times higher than those of recently reported FeO x and CoO x NPs on YSZ 25,26 but was still lower than that of ruthenium, a noble metal catalyst. 21…”

“…Panaritis et al 25 illustrated that the oxidation state of FeO x /YSZ could be controlled by the application of a small current or potential and thereby influenced the RWGS reaction rate. Similarly, Zagoraios et al 26 showed an EPOC effect for RWGS reaction by using CoO x /YSZ, which also possessed multiple oxidation states. Both Fe and Co showed comparable enhancement performance to noble metals, but the steady-state reaction rates under open-circuit potential were still inferior and the promotion phenomenon was not stable, accompanied by rapid changes in the beginning and end of polarizations.…”

“…Moreover, metals including Ru, Pd, Ni, Co, and Fe dispersed on various solid electrolytes like Y 2 O 3 -doped barium zirconate (BZY, H + conductor), Y 2 O 3 -stabilized ZrO 2 (YSZ, O 2− conductor), and β′′-Al 2 O 3 (Na + or K + conductor) have been used as catalysts in CO 2 hydrogenation. 21–26 In EPOC, promoting ion species are supplied to or removed from catalyst electrochemically by polarizing between counter electrode and catalyst which also functions as the working electrode. 11 Positive polarization refers to applying a positive potential difference between the working and the reference electrodes ( U WR > 0) or passing current from the working electrode to the counter electrode, and negative polarization is referred to the opposite situation.…”

Electrochemical control of the RWGS reaction over Ni nanoparticles deposited on yttria stabilized zirconia

“…A promising method to obtain high RWGS activity is through the use of the electrochemical promotion of catalysis (EPOC) effect and the in situ electro-oxidation of non-noble transition metals. 21 More specifically, the EPOC effect, also known as non-faradaic electrochemical modification of catalytic activity (NEMCA) is a highly utilized tool in heterogeneous catalysis over the past 40 years. [22][23][24][25][26][27] This effect is commonly studied with a simple and straightforward experimental set up involving three metal electrodes deposited onto a solid electrolyte/ion conductor as shown in Fig.…”

Mechanochemical redox synthesis of interstitial mesoporous CoxFe1‐xOy catalyst for CO2 hydrogenation

“…Herein, Co x Fe 1‐ x O y has been prepared through simple ball milling (BM method), a facile mechanochemical redox method, and a series of catalysts with high surface area (131 m 2 g −1 ) was obtained, much higher than those of samples prepared via SG method (33 m 2 g −1 ) and CP method (49 m 2 g −1 ). The obtained‐catalysts were applied in the reverse water‐gas shift (RWGS) reaction, one of the most effective, essential, economical, and sustainable ways to utilize CO 2 waste by CO 2 hydrogenation 34,35 . The conversion rate of the hydrogenation catalyzed by Co x Fe 1‐ x O y in BM method was about 43% at 500 ℃, and the rates only reached 13.8% and 15.7% for the catalysts fabricated by SG method and CP method respectively under the same condition, indicating the mechanochemical redox process provides scope to extraordinary characteristics of the catalysts.…”