Unlocking high catalytic activity of mesoporous phytic acid-doped poly(m-phenylenediamine) for electrochemical reduction of biomass-derived cinnamaldehyde to 3-phenylpropanol

The design of metal-free electrocatalysts for efficient biomass-based cinnamaldehyde (CAL) conversion to high-value-added 3-phenylpropanol (HCOL) and the insight into their catalytic mechanism have drawn considerable attention. However, they remained challenging due to the unclear complicated hydrogenation pathways. Here, metal-free mesoporous polymer-based electrocatalysts were synthesized, for the first time, for the electrochemical hydrogenation of CAL to HCOL. The catalysts consist of phytic acid (PA)-doped mesoporous poly(m-phenylenediamine) (coined meso-PA/PmPD) with high specific surface areas up to 95.3 m²/g. The optimized meso-PA/PmPD exhibits a record-high performance with high Faradaic efficiency (93.5%) and selectivity (97.5%), far surpassing all the reported electrocatalysts (Faradaic efficiency < 55% and selectivity < 25%). Mechanistic studies reveal that meso-PA/PmPD induces the parallel-configuration adsorption of CAL via π–π and hydrogen-bonding interactions, reducing the energy barriers for CAL carbonyl hydrogenation with active hydrogen ( $\mathrm{H}\text{*}$) to COL and its subsequent hydrogenation to HCOL, thereby boosting the HCOL selectivity. Meanwhile, an appropriate PA doping amount accelerates water dissociation to generate $\mathrm{H}\text{*}$ and interfacial charge transfer. The mesoporous structure facilitates CAL mass transport into the catalyst interior to promote its conversion. This study provides novel insight into the electroreduction mechanism of CAL, guiding the design of high-performance biomass-conversion electrocatalysts through rationally structural engineering of porous polymers.