Aminosilanized Interface Promotes Electrochemically Stable Carbon Nitride Films with Fewer Trap States on FTO for...

We have demonstrated the direct growth of a CN layer on a plasma-cleaned and aminosilanized F-doped SnO₂ (FTO) electrode to study the CN|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 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 polymer condensation, thus generating a thinner and more compact CN layer. The modification at the interface was shown to influence the CN growth on length scales of tens of micrometers. We grew CN thin films on p-FTO_NH2 (CN/p-FTO_NH2) and nonaminosilanized p-FTO (CN/p-FTO). CN/p-FTO_NH2 had a smaller density of trap states and passed 2.4 times the charges before failure compared to CN/p-FTO. Additionally, a 40% decrease in interfacial charge transfer resistance at the CN|electrolyte interface was measured for CN/p-FTO_NH2 compared to CN/p-FTO under -0.5 V vs RHE in 0.1 M Na₂SO₄. Furthermore, with the CN surface coated with a Pt cocatalyst, Pt/CN/p-FTO_NH2 exhibited faster hydrogen evolution rates and larger current densities than Pt/CN/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/p-FTO_NH2, Pt/CN/p-FTO, CN/p-FTO_NH2, and CN/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|FTO interface and suggested potential solutions to make CN films better (photo)electrodes for (photo)electrochemical systems.