Role of Heteroatoms in S,N‐Codoped Nanoporous Carbon Materials in CO₂ (Photo)electrochemical Reduction

Abstract

Thiourea-modified wood-based activated carbon materials were evaluated as catalysts for the CO electrochemical reduction reaction (CO ERR). The materials obtained at 950 °C showed long-term stability. The results indicated that thiophenic sulfur provides the catalytic activity for CO formation. However, it was not as active for CH formation as was pyridinic N. Tafel plots suggested that the nanoporous structure enhanced the kinetics for CO reduction. The electric conductivity limited the activity for CO ERR in the materials modified at 600, 800, and 900 °C. The effect of visible light on CO ERR was also investigated in this study. Upon irradiation, photocurrent was generated, and the current density increased during the CO reduction process. Combined with a band-gap alignment, the results indicate that thiophenic S in the carbon matrix contributed to the sample's photoactivity in visible light. These species enhance the overall reduction process, promoting both the hydrogen evolution reaction and CO reduction to CO.

Roles of Oxygen Functional Groups in Carbon Nanotubes‐Supported Ag Catalysts for Electrochemical Conversion of CO2 to CO

“…The alkali consumption of CNT−COOH is the highest to arrive a certain pH since it has the strongest proton‐donating ability among the three samples followed by CNT−OH and CNT−CO. Normally, strong acidic groups (mainly carboxyl groups) display p K a <7 and hydroxyl groups attached to large polyaromatic rings show p K a of 8∼9 . The amounts of acidic groups within different ranges of p K a have been calculated from the differences between the titration curves for blank and CNTs (Table S3).…”

Photoinduced Oxygen Reduction Reaction Boosts the Output Voltage of a Zinc–Air Battery

“…[6] However,o wing to the huge polarization of the oxygen reduction reaction (ORR), the attainable output voltage is 1.38 Vath ighest, [7] thus leading to low energy density,w hich equals the output voltage multiplied by the specific capacity.V arious electrocatalysts have been tested in attempts to reduce the polarization of ORR and hence raise the output voltage of Zn-air batteries. [8][9][10] Fore xample,n oble metals and their alloys, [8] spinel transition-metal oxides, [9] metal nitrides, [10] and carbon materials have been developed as cathode electrocatalysts for Zn-air batteries.H owever, even with the state-of-the-art electrocatalyst of Pt supported on carbon black (Pt/C), the achievable output voltage is still 260 mV lower than the theoretical value.Incorporating light into Zn-air batteries to accelerate the sluggish ORR or increasing the discharge voltage for high energy density will be challenging and meaningful.Photoinduced electrochemical reduction of small molecules has been actively studied, [11] and the results suggest strong reductive capability of the photoelectrons generated in semiconductors.Inthis study,polytrithiophene (pTTh) [12] was electrochemically deposited on carbon paper (CP) and employed as ap hotoelectrode in Zn-air batteries.U pon irradiation, photoelectrons are generated in the conduction band (CB) of pTThand accepted by O 2 molecules to generate HO 2 À ,w hich is disproportioned to OH À and O 2 to drive oxidation of Zn to ZnO at the anode.The output voltage is as high as 1.78 Va nd surpasses the thermodynamic limit of aconventional Zn-air battery.The photoinduced ORR at the pTThc athode enables the direct conversion of solar energy into electric energy in aZ n-air battery,t hus leading to an intrinsically different reaction scheme,and boosts the energy density. Figure 1a displays the scanning electron microscopy (SEM) image of the as-synthesized pTThbye lectrochemical polymerization of trithiophene (TTh; see Figure S1 in the Supporting Information).…”

“…Photoinduced electrochemical reduction of small molecules has been actively studied, [11] and the results suggest strong reductive capability of the photoelectrons generated in semiconductors.Inthis study,polytrithiophene (pTTh) [12] was electrochemically deposited on carbon paper (CP) and employed as ap hotoelectrode in Zn-air batteries.U pon irradiation, photoelectrons are generated in the conduction band (CB) of pTThand accepted by O 2 molecules to generate HO 2 À ,w hich is disproportioned to OH À and O 2 to drive oxidation of Zn to ZnO at the anode.The output voltage is as high as 1.78 Va nd surpasses the thermodynamic limit of aconventional Zn-air battery.The photoinduced ORR at the pTThc athode enables the direct conversion of solar energy into electric energy in aZ n-air battery,t hus leading to an intrinsically different reaction scheme,and boosts the energy density. Figure 1a displays the scanning electron microscopy (SEM) image of the as-synthesized pTThbye lectrochemical polymerization of trithiophene (TTh; see Figure S1 in the Supporting Information).…”

Importance of Carbon Porosity for Energy-Related Applications

“…The objective of this minireview is to summarize our recent findings on the importance of porosity of carbons for energy related applications. The examples of the performance of porous carbon in these applications concern ORR and CO 2 electroreduction [13][14][15][16][17][18]. Even though for these processes surface chemistry is of paramount importance, our results indicate the small pores can contribute markedly to the efficiency of these target processes.…”

“…The author is grateful to all students and collaborators listed in Ref. [13][14][15][16][17][18] for their contributions to this research.…”