Thiophene‐Based Conjugated Acetylenic Polymers with Dual Active Sites for Efficient Co‐Catalyst‐Free Photoelectrochemical Water Reduction in Alkaline Medium

Abstract

Although being attractive materials for photoelectrochemical hydrogen evolution reaction (PEC HER) under neutral or acidic conditions, conjugated polymers still show poor PEC HER performance in alkaline medium due to the lack of water dissociation sites. Herein, we demonstrate that tailoring the polymer skeleton from poly(diethynylthieno[3,2‐b]thiophene) (pDET) to poly(2,6‐diethynylbenzo[1,2‐b:4,5‐b′]dithiophene (pBDT) and poly(diethynyldithieno[3,2‐b:2′,3′‐d]thiophene) (pDTT) in conjugated acetylenic polymers (CAPs) introduces highly efficient active sites for water dissociation. As a result, pDTT and pBDT, grown on Cu substrate, demonstrate benchmark photocurrent densities of 170 μA cm−2 and 120 μA cm−2 (at 0.3 V vs. RHE; pH 13), which are 4.2 and 3 times higher than that of pDET, respectively. Moreover, by combining DFT calculations and electrochemical operando resonance Raman spectroscopy, we propose that the electron‐enriched Cβ of the outer thiophene rings of pDTT are the water dissociation active sites, while the −C≡C− bonds function as the active sites for hydrogen evolution.

Visible Light‐Driven Selective Reduction of CO2 by Acetylene‐Bridged Cobalt Porphyrin Conjugated Polymers

“…In addition, the CoPor‐DBBP shows a lower Δ G barrier than that of CoPor‐BBPA for process of CO* desorption to form free CO molecules, implying CoPor‐DBBP would exhibit a higher CO generation rate in thermodynamics. As for H 2 evolution, the C atom in acetylene bond serves as active center basing on reported works [17] . As overserved in Figure 6b, the Δ G value for CoPor‐BBPA is 5.77 kcal mol −1 , much lower than that of CoPor‐DBBP (33.90 kcal mol −1 ), manifesting CoPor‐BBPA possibly favor more efficient H 2 generation.…”

“…To elaborate the local chemical structures of CoPor‐DBBP and CoPor‐BBPA, Fourier‐transform infrared (FTIR) spectroscopy was adopted. As shown in Figure 1a, the obtained materials displayed the characteristic signals of C≡C stretching vibration bands at 2192 cm −1 [17] . In addition, the N−H stretching bands in region of 3100–3400 cm −1 are greatly attenuated, while new characteristic peaks of Co−N vibration at 1701 cm −1 was observed, indicating that Co II was successfully coordinated to porphyrin ring.…”

“…As for H 2 evolution, the C atom in acetylene bond serves as active center basing on reported works. [17] As overserved in Figure 6b, the ΔG value for CoPor-BBPA is 5.77 kcal mol À 1 , much lower than that of CoPor-DBBP (33.90 kcal mol À 1 ), manifesting CoPor-BBPA possibly favor more efficient H 2 generation. The theoretical calculations indicate that CoPor-DBBP is more favorable for the evolution of CO and inhibition of H 2 generation, which coincided well the experimental results.…”

“…As shown in Figure 1a, the obtained materials displayed the characteristic signals of C�C stretching vibration bands at 2192 cm À 1 . [17] In addition, the NÀ H stretching bands in region of 3100-3400 cm À 1 are greatly attenuated, while new characteristic peaks of CoÀ N vibration at 1701 cm À 1 was observed, indicating that Co II was successfully coordinated to porphyrin ring. The chemical structures of acetylene-bridged porphyrin conjugated polymers were further verified by the solid-state cross-polarization magic angle spinning (CP/MAS) 13 C NMR spectra.…”

Molecular Engineering of Photocathodes based on Polythiophene Organic Semiconductors for Photoelectrochemical Hydrogen Generation

“…The current pTH-involved photocathodes for solar hydrogen production are primarily based on polymer–fullerene bulk heterojunction architectures, − in which the photogenerated electrons from the excited bulk heterojunction arriving at the electrode/liquid electrolyte interface are relayed to a catalyst for the hydrogen evolution reaction (HER). However, electrolyte ion and water intercalation affect the charge transport, reactivity, and stability in these systems. − Recently, conjugated polymer pTH-based single-junction photocathodes exhibited considerable activity for HER and stability over days of continuous use, indicating a significant application potential for pTH-based single-junction architectures in solar hydrogen production. − Unfortunately, in these cases, dozens of microampere photocurrents are unsatisfactory. Applying molecular engineering with scientific methods could provide feasible solutions to improve the performance of pTH-based single-junction photocathodes …”