3D printer fabrication of boron doped Cu-MWCNT/PLA electrodes: Investigation of its efficiency in electrocatalytic hydrogen production

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In this study, three-dimensional (3D) electrodes based on MWCNT-Cu/PLA with high electrocatalytic efficiency, large surface area and different amounts of nano‑boron doped MWCNT-Cu/PLA were fabricated using Fused Granular Fabrication (FGF) method with a 3D printer. When FE-SEM images are examined, MWCNT fibers and copper particles are seen more clearly on the surface due to the formation of more dense conductive networks between the conductive carbon fibers trapped in the PLA structure due to the increasing amount of boron. When XRD results are examined, it is observed that the characteristic peaks belonging to the face-centered cubic structure of Cu are dominant and the crystal size increases as MWCNT addition and boron doping increase. When Raman spectra were analyzed to investigate the internal structural changes of MWCNTs, three characteristic bands corresponding to the D band (defect), G band (graphite band) and G' band (D overtone) of MWCNTs were determined and it was observed that the ID/IG ratio decreased with increasing boron doping compared to MWCNT-Cu/PLA electrode. The B1s spectrum of the 3D 0.8B@MWCNT-Cu/PLA electrode confirmed the presence of boron with the peak corresponding to B@C bonds at 191.2 eV. The obtained 3D electrocatalysts were used as cathodes in an electrolysis cell in aqueous solution containing 1 M KOH and their catalytic efficiency in hydrogen evolution reaction (HER) was tested. In order to increase the activity of the 3D electrodes, unlike the literature, they were activated by electrochemical activation process without using organic solvent and HER measurements of the activated electrodes were performed. Before activation, the charge transfer resistance (Rct) value of the Cu/PLA electrode, which was 6219.00 Ω cm−2, decreased to 681.90 Ω cm−2 after 5 % MWCNT doping. It is seen that with boron doping, a greater decrease in Rct value is realized, reaching values of 66.50–74.56 Ω cm−2. The cathodic Tafel slopes show that the Volmer reaction is the rate-determining step for HER and the rate-determining step is the electrochemical adsorption of hydrogen on the metal surface. In addition, energy efficiency tests of the 3D electrodes in HER were also performed and electrochemically active surface areas were determined. Thus, this study has taken an important step toward using 3D electrocatalysts, which are produced with more cost and more flexible designs, unlike previous production techniques, for hydrogen energy production.