Chemical manufacturing significantly contributes to greenhouse gas emissions and energy consumption. Valorizing biomass-based substrates to produce valuable chemicals offers a sustainable alternative to fossil fuels. 5-Hydroxymethylfurfural (HMF), a key biomass-derived intermediate, can be upgraded to various high-value chemicals, including 2,5-bis(hydroxymethyl)furan (BHMF), which is crucial in various industrial applications. Current industrial BHMF production relies on thermocatalytic routes using precious metal catalysts and harsh conditions, raising environmental and energy concerns. Electrocatalytic HMF hydrogenation (ECH) offers a greener approach, using water as a hydrogen source under ambient conditions. However, challenges include the formation of undesired byproducts and the competing hydrogen evolution reaction (HER). Existing high-performing electrodes often contain precious metals. This research aims to develop an efficient and sustainable electrocatalyst based on earth-abundant elements for the electrochemical conversion of HMF to BHMF. The study focuses on the in-situ surface reconstruction of two-dimensional (2D) materials, specifically CdPS3 nanosheets, to improve catalytic activity and selectivity. The rich sulfur and phosphorus environment in MPS3 is hypothesized to provide structural flexibility and enable surface reconstruction, exposing numerous active sites to enhance the reaction.

Numerous studies have explored electrocatalytic HMF hydrogenation, often using precious metals like Ag and Cu to achieve reasonable selectivity to BHMF while minimizing HER. However, the development of catalysts based on earth-abundant elements is crucial for practical application. The rational design of electrocatalysts requires a thorough understanding of the reaction process and surface/interface control. Research has highlighted the importance of dynamic electrode surfaces and in-situ generated active species in manipulating the adsorption energetics of reaction intermediates and boosting catalytic activity. Two-dimensional materials have shown promise in electrocatalytic biomass conversion. This research builds upon previous work on the growth of 2D MPS3 nanosheet arrays and their potential for surface reconstruction to enhance product selectivity, a feature not extensively explored in earlier studies.

Ultrathin CdPS₃ nanosheets were synthesized on a carbon cloth substrate via a two-step solvothermal-space confined chemical vapor conversion process. The process involved synthesizing a CdS nanoparticle precursor followed by conversion to CdPS₃ nanosheets. The synthesized material was characterized using various techniques, including XRD, Raman spectroscopy, TEM, HR-TEM, AFM, and XPS to confirm the structural and morphological properties. Electrocatalytic activity towards HMF hydrogenation was evaluated using linear sweep voltammetry (LSV), chronoamperometry, and electrochemical impedance spectroscopy (EIS) in a three-electrode system using 0.1 M phosphate buffer solution (PBS, pH 9.2) containing 10 mM HMF. The Faradaic efficiency (FE) and BHMF yield were calculated. In-situ Raman spectroscopy was employed to monitor structural evolution during electrochemical HMF hydrogenation. Ex-situ XRD, XPS, SEM, and HR-TEM were used for post-mortem analysis to confirm surface reconstruction. Density functional theory (DFT) calculations were performed to investigate the reaction mechanism and the role of the in-situ generated CdS layer. A two-electrode system was constructed by pairing the CdPS₃ cathode with a MnCo₂O₄ anode for simultaneous BHMF and formate synthesis from HMF and glycerol. The MnCo₂O₄ anode was also characterized using SEM, TEM, and EIS.

The CdPS₃ nanosheet electrocatalyst exhibited exceptional performance in electrochemical HMF hydrogenation, achieving a high Faradaic efficiency (FE) of 91.3 ± 2.3% for BHMF synthesis with a yield of 4.96 ± 0.16 mg/h at -0.7 V versus RHE. In-situ Raman spectroscopy and ex-situ characterizations provided strong evidence for the formation of a CdPS₃/CdS heterostructure due to in-situ surface reconstruction, triggered by the PBS electrolyte. The reconstruction process was not observed in borate buffer solution (BBS), highlighting the electrolyte's crucial role. DFT calculations revealed that the in-situ generated CdS layer plays a critical role in optimizing the adsorption of HMF* and H*, reducing energy barriers for key intermediates, and facilitating HMF hydrogenation through a Langmuir-Hinshelwood (LH) mechanism, favoring the O-pathway. The CdPS₃/CdS heterostructure demonstrated excellent stability over seven cycles. Coupling the CdPS₃/CdS cathode with a MnCo₂O₄ anode in a two-electrode system enabled the simultaneous synthesis of BHMF and formate from HMF and glycerol, achieving FEs of 67.7% and 75.25%, respectively, at a low cell voltage of 1.9 V. Control experiments using In2S3 and CdPSe3 nanosheets showed no surface reconstruction and significantly lower catalytic activity, highlighting the unique behavior of CdPS3.

This study successfully demonstrated the use of in-situ surface reconstruction of CdPS₃ nanosheets to create a highly efficient electrocatalyst for BHMF synthesis. The findings address the challenge of developing sustainable and efficient electrocatalysts for biomass upgrading. The superior performance of the CdPS₃/CdS heterostructure compared to pristine CdS or other 2D materials underlines the significance of the in-situ generated interface. The combined experimental and theoretical results provide a comprehensive understanding of the structure-activity relationship, revealing how the reconstructed surface optimizes reactant and intermediate adsorption, leading to high selectivity and activity. The demonstration of paired electrochemical synthesis of BHMF and formate further enhances the sustainability and economic viability of the process. This work offers a new avenue for designing advanced electrocatalysts for biomass valorization, impacting green chemical manufacturing.

This research successfully synthesized a highly efficient CdPS₃ nanosheet electrocatalyst for BHMF production via electrochemical HMF hydrogenation. In-situ surface reconstruction leading to a CdPS₃/CdS heterostructure was identified as the key to enhanced performance. DFT calculations clarified the mechanism. Coupled electrochemical synthesis with a MnCo₂O₄ anode enabled simultaneous BHMF and formate production. This study provides valuable insights into catalyst design for biomass valorization and sustainable energy applications. Future studies could explore different 2D materials, investigate the influence of various electrolytes, and optimize the two-electrode system for enhanced efficiency and broader substrate compatibility.

The study focused primarily on HMF hydrogenation and glycerol oxidation. The generalizability of the in-situ reconstruction phenomenon to other biomass substrates needs further investigation. While the catalyst demonstrated good stability, long-term durability testing under industrial conditions is needed. The DFT calculations, while providing valuable insights, are based on simplified models, and some approximations may affect the accuracy of the calculated energy barriers.