NSRRC Activity Report 2023

028 NSRRC ACTIVITY REPORT 2023 A nanocomposite composed of carbon nanotubes adorned with copper and barium (CuBaCNT) was designed to elevate catalyst conductivity, alter the 3d orbitals of Cu (validated through 1s3p resonant inelastic X-ray scattering at SP 12U1 ), and augment selectivity and current density. 2 CuBaCNT demonstrated a Faradaic efficiency of 70.9% and a partial current density of 354.6 mA cm −2 for C 2 products at 500 mA cm −2 . This outperformed CuCO 3 , which exhibited a Faradaic efficiency of 67.8% and a partial current density of 203.3 mA cm −2 for C 2 products at 300 mA cm −2 . Operando X-ray absorption near edge structure (XANES) experiments conducted at the TLS 17C1 unveiled the swift reduction of Cu in CuBaCNT during CO 2 RR ( Fig. 1(a) ). The analysis of valence states that employs the zero crossing of the second derivative of the spectra suggested a valence state from +1.9 to +0.5 at –0.4 V vs RHE, which transitions into a metallic state at a more negative voltage. This transformation was attributed to the incorporation of carbon nanotubes, which improved overall conductivity and established a conductive network facilitating efficient electron transport to the electrocatalysts. Consequently, the authentic form of the catalyst during CO 2 RR appeared to be metallic Cu rather than CuCO 3 , which is the original composition of CuBaCNT. In addition to enhancing catalyst conductivity, establishing a stable interface between Cu 0 and Cu + within the catalyst represents a promising strategy for elevating catalytic activity. A method for achieving this stable interface involved the creation of rich nanograin boundaries through the thermal reduction of Cu 2 O nanocubes in a carbon monoxide (CO) atmosphere, referred to as Cu 2 O(CO). 3 This catalyst demonstrated a Faradaic efficiency of 77.4% and a partial current density for C 2+ products at 387.0 mA cm −2 at 500 mA cm −2 , which surpass those of bare Cu 2 O, which exhibited a Faradaic efficiency Fig. 2 : (a) Operando EXAFS spectra for CuPc/CNP and EDTA/CuPc/CNP during CO 2 RR. (b) Operando X-ray absorption spectroscopy during CO 2 RR and under an Ar atmosphere (200 mA cm −2 ). [Reproduced from Refs. 4 and 5] of 61.5% and a partial current density of 184.5 mA cm −2 for C 2+ products at 300 mA cm −2 . Operando XANES experiments conducted at the SP 12B1 were employed to validate the impact of nanograin boundaries on Cu 0 /Cu + interfacial sites within the Cu 2 O(CO) electrocatalyst during CO 2 RR. The linear recombination fitting results of XANES in Fig. 1(b) revealed that Cu 2 O(CO) consisted of 77.5% metallic Cu and 22.5% Cu 2 O before CO 2 RR, while over 20% Cu 2 O still remained during CO 2 RR. This observation indicated that the considerable presence of nanograin boundaries in the Cu 2 O(CO) electrocatalyst effectively impeded the reduction of Cu to a metallic state, thereby enhancing catalytic stability. Both particle size and coordination play crucial roles in determining the selectivity of CO 2 RR. A Cu catalyst with low coordination can effectively limit C–C coupling, promoting CO 2 methanation. A recent design approach utilized carbon nanoparticles (CNPs) and multi-dentate coordination using ethylenediaminetetraacetic acid (EDTA) to control the size of Cu clusters derived from the copper phthalocyanine (CuPc) precursor, showcasing its performance in acidic CO 2 RR for methane production. 4 Constrained by EDTA, EDTA/CuPc/ CNP achieved a Faradaic efficiency of 71% and a partial current density of 71 mA cm −2 at 100 mA cm −2 toward CH 4 . In contrast, EDTA/CuPc exhibited a lower Faradaic efficiency toward CH 4 at 48.9%, coupled with higher C 2 H 4 production. This emphasizes