Fabrication of Nanostructured Palladium Within Tridentate Schiff-Base-Ligand Coordination Architecture: Enhancement of Electrocatalytic Activity Toward CO2 Electroreduction

Abstract

There has been growing interest in the electrochemical reduction of carbon dioxide (CO 2 ), a potent greenhouse gas and a contributor to global climate change, and its conversion into useful carbon-based fuels or chemicals [1][2][3][4][5]. Numerous homogeneous and heterogeneous catalytic systems have been proposed to induce the CO 2 reduction and, depending on the reaction conditions (applied potential, choice of buffer, its strength and pH, local CO 2 concentration, or the catalyst used) various products that include carbon monoxide, oxalate, formate, carboxylic acids, formaldehyde, acetone, or methanol, as well as such hydrocarbons as methane, ethane, and ethylene, are typically observed at different ratios. These reaction products are of potential importance to energy technology, food research, medical applications, and fabrication of plastic materials.Given the fact that the CO 2 molecule is very stable, its electroreduction processes are characterized by large overpotentials, and they are not energy efficient. To produce highly efficient and selective electrocatalysts, the transitionmetal-based molecular materials are often considered [6][7][8]. The latter systems are capable of driving multi-electron transfers and, in principle, produce highly reduced species. In reality, such multi-electron charge transfer catalysts tend to effectively induce the two-electron reduction of CO 2 to CO rather than yield highly reduced products in large amounts. Metallic copper electrodes are unique in this respect because they can drive multi-electron transfers. Mechanisms of the successful electrochemical reductions of CO 2 to methane and ethylene can be interpreted in terms of complex processes occurring at copper electrodes [9,10]. It is believed that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate [11]. Significant decrease of the reaction overpotentials can be achieved with the use of the metal complex modified electrodes capable of both mediating electron transfers and stabilizing the reduced products [12].Because reduction of CO 2 can effectively occur by hydrogenation [13], in the present work, we concentrate on such a model catalytic system as nanostructured metallic palladium capable of absorbing reactive hydrogen in addition to the ability to adsorb monoatomic hydrogen at the interface [14][15][16]. Under such conditions, the two-electron reduction of CO 2 typically to CO [12] is favored. When the reaction proceeds on palladium in aqueous KHCO 3 solutions, carbon monoxide together with hydrogen and small amounts of formate are produced [17][18][19]. Further, it has been postulated that CO and COOH adsorbates are expected to be formed at the surfaces of Pd electrodes at −1.0 V (vs. Ag/AgCl) and, subsequently, desorbed at even more negative potentials [20].To produce highly dispersed and stabilized palladium nanoparticles (as for Fig. 1a), we have generated them by electrodeposition (through consecutive potential cycling) from the thin film of...

Visible-light-driven CO2reduction on dye-sensitized NiO photocathodes decorated with palladium nanoparticles

“…4 illustrates the cyclic voltammograms recorded for the nPd deposited (loading, 100 mg cm À2 ) on the glassy carbon electrode substrate in the argon-saturated 0.1 mol dm À3 Na 2 SO 4 in the presence (solid line) and absence (dashed line) of CO 2 . It is well established that in a model acid medium such as in 0.5 mol dm À3 H 2 SO 4 , the deposits of nPd exhibit characteristic hydrogen sorption/desorption peaks (below 0.25 V) 40,62,63 that are also observed here, as well as Pd oxide formation or reduction (above 0.55 V) peaks. In the near-neutral deoxygenated Na 2 SO 4 solution, the sorption of hydrogen (water reduction or proton discharge) is pushed to more negative potentials and starts at about À0.2 V (Fig.…”

“…While various noble metal heterogeneous catalysts have been examined, palladium nanoparticles could be considered as the stateof-the-art electrocatalysts for CO 2 RR predominantly to CO and, sometimes, to formate. [40][41][42][43][44][45] The unique interactions of CO 2 with Pd, capable of both absorbing and adsorbing hydrogen, are known to favor distinct reaction pathways that affect both the activity and selectivity of CO 2 RR relative to HER. The design of such photoelectrode materials must be carefully realized in order to favor the intended redox cascade between the components and to minimize competitive charge transfers that reduce the efficiency of the photocathode.…”

Carbon Dioxide Electroreduction at Highly Porous Nitrogen and Sulfur Co-Doped Iron-Containing Heterogeneous Carbon Gel

“…To elucidate catalytic activity of the Fe-NS-C carbon gel toward CO 2 electroreduction, cyclic voltammograms have been recorded in 0.1 mol dm −3 KHCO 3 (before and after saturation with CO 2 ) in the potential range extended down to more negative values covering the hydrogen evolution region (Figure 5a). Contrary to the performance of Pd-based catalysts, 2,19 there is no clear response which could be attributed to CO 2 reduction here ( Figure 5, red curves). Nevertheless, the observed reduction currents could originate from the proton-induced processes (e.g.…”

“…2,[16][17][18][19] Another important practical issue is related to the need of lowering costs of catalysts by substituting the noble metals with inexpensive abundant elements. There has been growing interest in catalysts based on nanostructured carbons that include the metal-free Ndoped systems and the metal-containing carbons.…”

“…Due to existence of two strong C=O bonds in the CO 2 molecule, its electroreduction requires high overpotentials, and the low reaction efficiency still remains fundamental problem limiting practical applications. [1][2][3] During recent years, various catalysts, including noble and non-noble transition metals, as well as their numerous coordination compounds, have been considered as catalysts for CO 2 electroreduction. [4][5][6][7][8][9][10] It has been demonstrated that selectivity of the process depends largely on the activating adsorptive (CO 2 ) phenomena and the affinity of catalytic centers to adsorbed carbon monoxide intermediate.…”