Efficient photoelectrocatalytic conversion of CO₂ to formic acid using Ag-TiO₂ nanoparticles formed on the surface of nanoporous structured Ti foil

Global warming and adverse climate change, which have been intensified by a strident increase in carbon dioxide (CO₂) emissions, have necessitated the development of alternative techniques to reduce the disproportionate concentration of CO₂ in the atmosphere. The photoelectrochemical reduction of CO₂ is a technique of lowering the energy required to convert greenhouse gases into useful end products. Herein, we have manufactured an innovative, cost-effective silver (Ag) decorated anatase TiO₂ (TO-Agx; ‘x’ stands for different concentration of Ag) nanoparticles which created on the 3D nanoporous structured surface of a thin titanium foil (Ti-foil) by the assist of chemical treatment with hydrogen peroxide (H₂O₂) and different concentrations (1, 5, 10, 20 mM) of silver nitrate (AgNO₃) solution and followed by calcination at 500 °C. As-prepared samples were analyzed by several characterization techniques such as XRD, XPS, TEM and Raman spectroscopy. Among various samples (TO, TO-Ag₁, TO-Ag₅, TO-Ag₂₀), the TO-Ag₁₀ sample were exposed a supreme photocurrent density of 83.2 µA/cm⁻² (86.1% higher than TO sample which is untreated with AgNO₃ solution). Because of its high photocurrent density, the sample TO-Ag₁₀ were selected as the electrode material for photoelectrochemical CO₂ reduction reaction and a lowest reduction onset potential (−1.018 V) was observed on linear sweep voltammetry analysis in the presence of light with Ag/AgCl reference electrode. ¹H NMR analysis of the product solution exposed the production of formic acid as a single product of CO₂ reduction reaction after the chronoamperometric electrolysis were carried out more than 6 h. The maximum faradaic efficiency (73%) and formic acid yield (193 µmol cm⁻² h⁻¹) were found at an applied potential of −1.2 V (vs. Ag/AgCl reference electrode) for TO-Ag₁₀ photocathode.