A Cu foam cathode used as a Pt–RGO catalyst matrix to improve CO₂ reduction in a photoelectrocatalytic cell with a TiO₂ photoanode

Abstract

Cu foam combined with Pt-modified reduced graphene oxide (Pt-RGO) was investigated as an efficient cathode for CO 2 reduction in a photoelectrocatalytic (PEC) cell with a TiO 2 nanotube (TNT) photoanode. The synergistic catalytic mechanisms between photocatalysis and electrocatalysis in such a photoanode driven 2-electrode PEC cell were experimentally verified and theoretically analyzed. The dual functional Cu foam, as cathode electrode and Pt-RGO catalyst matrix, markedly increased the carbon atom conversion rate because of its well-defined porosity, large specific surface area, and in particular its affinity for CO 2 reduction to hydrocarbons. Combination of Cu foam matrix and Pt-RGO catalysts resulted in synergistic CO 2 reduction in the (Pt-RGO/Cu foam)||TNT PEC cell. Carbon atom conversion rate markedly increased to 4340 nmol/(h cm 2 ) by optimizing CO 2 reduction conditions in the PEC cell, including voltage applied through cell, Pt loading amount on RGO, and Pt-RGO loading amount on Cu foam. plants 1, 2 . However, CO 2 reduction into fuels is anticipated to be very challenging because of the necessary energy-consuming process consisting of multiple number proton-coupled electron-transfer steps 3, 4 . Recently, photoelectrocatalytic (PEC) systems for CO 2 reduction 5-8 have been widely studied as a promising approach to overcoming the high energy barrier of CO 2 conversion in an energy-efficient and environment friendly manner.The key point of CO 2 PEC reduction is to achieve a synergistic effect between photocatalysis and electrocatalysis.However, studies virtually concentrate on photo-enhanced electric-reduction or electric-enhanced photo-reduction previously 9 . The combination of photocatalysis and electrocatalysis doesn't achieve a real sense of synergistic function actually. Nowadays, research on the photo and electric synergistic catalytic reduction of CO 2 mainly focuses on semiconductor photocatalyst materials 10, 11 . Although some achievements have been made, CO 2 PEC reduction still suffers from low reactivity, low selectivity, and large energy consumption.The principle of PEC systems is based on the conversion of light energy into electricity within a cell involving two electrodes, of which at least one is made of a semiconductor. This electricity is then used for CO 2 conversion.In theory, there are three options for the arrangement of photo-electrodes in the assembly of PEC cells: (ⅰ) photocathode made of p-type semiconductor and anode made of metal 5, 6, 10, 11 ; (ⅱ) photoanode made of n-type semiconductor and cathode made of metal 7, 12, 13 ; (ⅲ) photoanode made of n-type semiconductor and photocathode made of p-type semiconductor 8 . The first use of photoelectrocatalysis for CO 2 reduction was reported over 30 years ago with a p-type photocathode in the first assembly form 14 . This photocathode driven form is simple, easy to manipulate and most widely studied. However, studies on this form are limited to the development and improvement of semiconductor catalysts responding to visible lig...

CO2 Reduction of Hybrid Cu2O–Cu/Gas Diffusion Layer Electrodes and their Integration in a Cu‐based Photoelectrocatalytic Cell

“…Note that in the first hour,h owever,t here is not an increase in the rate, but an apparent effect relatedt o the accumulation of the H 2 in the empty volumeo ft he gas phase system of the electrocatalytic reactor.B eing this side reaction of H 2 formation mainly due to the GDL itself, as commented before,i ti sr easonable to indicate that the active sites responsible of this side reaction are progressively inhibited, www.chemsuschem.org likely by CO 2 strong chemisorption. [63,66] Ad ecrease in the H 2 production with time, with an increasei nt he relative CO and hydrocarbons formation, was also reported by Peterson et al [67] They attributed this decrease to the changes in the speciesa dsorbed on the surface, consistent with the above interpretation. The Cu 2 O/GDL electrode used in CO 2 electrocatalytic reduction was characterized to monitor the changes occurred.…”

“…A drastic increase in faradaic selectivity of one order‐of‐magnitude for both formate and acetate is observed, with total carbon selectivity above 95 %. Even if acetate has been considered deriving from further reactions through coupling processes from the formed species with one carbon atom, the trends observed in Figure do not indicate a consecutive, but a parallel path for the two products. The hydrogen production reaches the higher amount in the first 1 h of CO 2 electroreduction, decreasing with time.…”

“…Note that in the first hour, however, there is not an increase in the rate, but an apparent effect related to the accumulation of the H 2 in the empty volume of the gas phase system of the electrocatalytic reactor. Being this side reaction of H 2 formation mainly due to the GDL itself, as commented before, it is reasonable to indicate that the active sites responsible of this side reaction are progressively inhibited, likely by CO 2 strong chemisorption . A decrease in the H 2 production with time, with an increase in the relative CO and hydrocarbons formation, was also reported by Peterson et al .…”

“…Ad rastic increase in faradaic selectivity of one order-of-magnitude for both formate and acetate is observed, with total carbon selectivity above 95 %. Even if acetate has been considered deriving from furtherr eactions throughc oupling processes from the formed species with one carbon atom, [63][64][65] the trendso bservedi nF igure 4d on ot indicate ac onsecutive, but ap arallel path for the two products.T he hydrogen production reaches the highera mount in the first 1hof CO 2 electroreduction,d ecreasingw ith time. Note that in the first hour,h owever,t here is not an increase in the rate, but an apparent effect relatedt o the accumulation of the H 2 in the empty volumeo ft he gas phase system of the electrocatalytic reactor.B eing this side reaction of H 2 formation mainly due to the GDL itself, as commented before,i ti sr easonable to indicate that the active sites responsible of this side reaction are progressively inhibited, www.chemsuschem.org likely by CO 2 strong chemisorption.…”

Recent progress on advanced design for photoelectrochemical reduction of CO2 to fuels

“…The optimization of Pt-RGO cathode induced an arresting enhancement of carbon atom conversion rate to 1.5 μmol h −1 cm −2 [170]. Replacing Ni foam with Cu foam as cathode substrate could further enhance the carbon atom conversion rate to 4.34 μmol h −1 cm −2 [171]. In addition to metal/carbon cathodes, some semiconductors have emerged as promising cathode materials for CO 2 reduction.…”