Bio-inspired synthesis of heterogeneous transition metal complexes and its catalytic activity towards energy applications

In this study, the modified cellulose-based compound enclosed with transition metal ions of K(I), Ba(II), Cd(II), Co (II), Ni (II), Cr(II), Mn(II), and Mg(II) in a 1:1:2 ratio was synthesized systematically. The formation of metal complexes was characterized using IR, UV–Vis, XRD, and thermal analysis. From FT-IR, it was evident that the isolation of cellulose from the wheat husk exhibited characteristic absorption bands, followed by distinct peaks in the range of 3300-3200 cm−1, owing to the OH stretching frequency of the carboxyl group and N-N stretching frequencies in the range of 1020–1060 cm−1. The asymmetric and symmetric stretching frequencies of carboxylate ions are observed in the ranges 1620-1627 cm−1 and 1350-1452 cm−1, respectively. The stretching vibration frequency of the M-O bond was observed below 1000 cm−1, which confirms the formation of the metal-oxygen bond and its binding ability. UV–visible spectral data confirms the existence of metal complexes in a distorted octahedral geometry with appropriate transitions. The thermal behavior of metal complexes confirms their degradation pattern, and the thermogram shows no additional exothermic or endothermic peaks, which implies the homogeneity and purity of the product formed. The application of the hydrogen evolution reaction was observed, where the charge transfer resistance (Rct) for the complexes was smaller, indicating higher hydrogen evolution reaction (HER) activity and higher catalytic performance. Minimum Tafel slope values in the range of 1.67 mV/dec imply the existence of active sites in the catalyst. Heyrovsky reaction proceeds with a kinetic barrier of 1.062 eV. Thus, electrocatalysts with the highest binding energy will exhibit stronger hydrogen adsorption, thereby improving electrode performance by decreasing the energy barrier.