Fabrication of Pd/MnFe₂O₄ bifunctional 2-D nanosheets to enhance the yield of HCOOH from CO₂ cathodic reduction paired with anodic oxidation to CH₃OH

Highly active and stabilized bifunctional electrocatalysts contributed to the reduction of hazardous atmospheric pollutants through paired electrochemical reactions. Herein, spherical-like Pd nanoparticles were successfully grown on two-dimensional MnFe₂O₄ nanosheets (2-D Pd/MnFe₂O₄ NSs) via microwave irradiation and tested in an electrochemical cell as dual-functional hybrid electrode material. Several characterization techniques were used to determine the morphological, structural and chemical properties of the as-prepared bifunctional Pd/MnFe₂O₄ electrocatalysts. The 2-D Pd/MnFe₂O₄ NSs exhibited a higher specific surface area of 390 m² g⁻¹ with a pore volume of 0. 327 cm³ g⁻¹, resulted in a high CO₂ reduction activity (CO₂ RR) towards the desired production of formic acid. The HCOOH yield was optimized by varying the cell potential, electrolyzer reaction time, and electrolyte concentration. The maximum yield of HCOOH was found to be 476 μmol h⁻¹ cm⁻² with a Faradic efficiency of (FE) 96.9%. Furthermore, CO₂ RR was coupled with CH₃OH oxidation reaction (CH₃OH OR) to evaluate the paired electrochemical activity of the bifunctional Pd/MnFe₂O₄ electrocatalysts. The results showed that Pd/MnFe₂O₄ had a high production rate of HCOOH of about 625 µmol h⁻¹ cm⁻² with FE of 97.5% at −1.0 V vs. RHE in optimized electrolyzer concentrations. During CH₃OH OR, many H⁺ and e⁻ were formed, which is the key to increasing HCOOH yield through the paired electrolyzer. The mechanism of the paired electrochemical reaction was also described in detail. This study showed that integrated future bifunctional fuel cells utilizing CH₃OH combined with CO₂ reduction strategies, could achieve zero gas exhaust emission and sustainably produce high value-added chemicals.