Aminosilanized Interface Promotes Electrochemically Stable Carbon Nitride Films with Fewer Trap States on FTO for (Photo)electrochemical Systems

Chang Liu; Stephanie Busse; Jian Liu; Robert Godin

doi:10.1021/acsami.3c09284

Aminosilanized Interface Promotes Electrochemically Stable Carbon Nitride Films with Fewer Trap States on FTO for (Photo)electrochemical Systems

ACS Appl Mater Interfaces. 2023 Oct 11;15(40):46902-46915. doi: 10.1021/acsami.3c09284. Epub 2023 Sep 29.

Authors

Chang Liu¹, Stephanie Busse¹, Jian Liu^{2

3}, Robert Godin^{1

3

4}

Affiliations

¹ Department of Chemistry, The University of British Columbia, 3247 University Way, Kelowna, BC V1V 1V7, Canada.
² School of Engineering, Faculty of Applied Science, University of British Columbia, Kelowna, BC V1V 1V7, Canada.
³ Clean Energy Research Center, University of British Columbia, 2360 East Mall, Vancouver, BC V6T 1Z3, Canada.
⁴ Okanagan Institute for Biodiversity, Resilience, and Ecosystem Services, University of British Columbia, Kelowna, BC V1V 1V7, Canada.

PMID: 37774114
DOI: 10.1021/acsami.3c09284

Abstract

We have demonstrated the direct growth of a CN_x layer on a plasma-cleaned and aminosilanized F-doped SnO₂ (FTO) electrode to study the CN_x|FTO interface that is critical for (photo)electrocatalytic systems. The (3-aminopropyl)triethoxysilane (APTES) was chosen as a bifunctional organosilane, with the amino end incorporating into CN_x and the silane end connecting to the hydroxylated FTO surface. Plasma cleaning and aminosilanization resulted in a highly hydrophilic surface, which leads to better contact of melted thiourea to the aminosilanized FTO (p-FTO_NH2) during CN_x polymer condensation, thus generating a thinner and more compact CN_x layer. The modification at the interface was shown to influence the CN_x growth on length scales of tens of micrometers. We grew CN_x thin films on p-FTO_NH2 (CN_x/p-FTO_NH2) and nonaminosilanized p-FTO (CN_x/p-FTO). CN_x/p-FTO_NH2 had a smaller density of trap states and passed 2.4 times the charges before failure compared to CN_x/p-FTO. Additionally, a 40% decrease in interfacial charge transfer resistance at the CN_x|electrolyte interface was measured for CN_x/p-FTO_NH2 compared to CN_x/p-FTO under -0.5 V vs RHE in 0.1 M Na₂SO₄. Furthermore, with the CN_x surface coated with a Pt cocatalyst, Pt/CN_x/p-FTO_NH2 exhibited faster hydrogen evolution rates and larger current densities than Pt/CN_x/p-FTO. The highest Faraday efficiency toward electrochemical hydrogen evolution (FE_H2) in 0.1 M Na₂SO₄ (pH = 7) was 46.1%, 37.3%, 57.7%, and 70.5% for Pt/CN_x/p-FTO_NH2, Pt/CN_x/p-FTO, CN_x/p-FTO_NH2, and CN_x/p-FTO, respectively. The increase in hydrogen evolution rate did not follow the magnitude of the current density change, indicating electrochemical processes other than proton reduction. Overall, we have carefully investigated the CN_x|FTO interface and suggested potential solutions to make CN_x films better (photo)electrodes for (photo)electrochemical systems.

Keywords: carbon nitride; electrochemical hydrogen evolution reaction; electrochemical impedance spectroscopy; electrochemical stability; faraday efficiency; surface aminosilanization; transient absorption spectroscopy; trap states.