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

We have demonstrated the direct growth of a CN x layer on a plasma-cleaned and aminosilanized F-doped SnO 2 (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 Na 2 SO 4 . 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 Na 2 SO 4 (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.