Metal Silicidation in Conjunction with Dopant Segregation: A Promising Strategy for Fabricating High-Performance Silicon-Based Photoanodes

Surface Reconstructed Ni0.95Pt0.05/Si Photoelectrodes for Bias-free Hydrogen Evolution Coupled with 5-hydroxymethylfurfural Oxidation

Coupling hydrogen evolution reaction (HER) with biomass valorization using a photoelectrochemical (PEC) system presents a promising approach for effectively converting solar energy to chemical energy. A crucial biomass valorization reaction is the production of value-added 2,5-furandicarboxylic acid (FDCA) via 5-Hydroxymethylfurfural (HMF) oxidation reaction (HMFOR). To achieve efficient FDCA production, we demonstrate an effective photoanode strategy that combines metal silicidation, dopant segregation, and surface reconstruction to create a bimetallic silicide Ni0.95Pt0.05Si/n-Si photoanode. The oxide-free Ni0.95Pt0.05Si/n-Si interface prepared by the metal-silicidation process ensures efficient interfacial charge transport, while dopant segregation enhances the Schottky barrier height and photovoltage, and surface reconstruction dramatically improves the catalytic activity of the photoanode surface. The as-prepared Ni0.95Pt0.05Si/n-Si photoanode exhibited excellent PEC performance for HMFOR with high conversion of HMF (97.2 %) and yield of FDCA (80.3 %) under illumination. Furthermore, by integrating a surface reconstructed Ni0.95Pt0.05Si/n-Si photoanode with a Ni0.95Pt0.05Si/p-Si photocathode, a dual-photoelectrode system was constructed capable of simultaneous production of FDCA and H2, which achieves high photocurrent density of 5 mA cm-2 at zero bias under illumination. This study offers an auspicious prospect for high cost-effectiveness conversion from solar energy to industrial monomers.

Dissolution-Induced Surface Reconstruction of Ni0.95Pt0.05Si/p-Si Photocathode for Efficient Photoelectrochemical H2 Production

Metal silicide/Si photoelectrodes have demonstrated significant potential for application in photoelectrochemical (PEC) water splitting to produce H2. To achieve an efficient and economical hydrogen evolution reaction (HER), a paramount consideration lies in attaining exceptional catalytic activity on the metal silicide surface with minimal use of noble metals. Here, this study presents the design and construction of a novel Ni0.95Pt0.05Si/p-Si photocathode. Dopant segregation is used to achieve a Schottky barrier height as high as 1.0 eV and a high photovoltage of 420 mV. To achieve superior electrocatalytic activity for HER, a dissolution-induced surface reconstruction (SR) strategy is proposed to in situ convert surface Ni0.95Pt0.05Si to highly active Pt2Si. The resulting SR Ni0.95Pt0.05Si/p-Si photocathode exhibits excellent HER performance with an onset potential of 0.45 V (vs RHE) and a high maximum photocurrent density of 40.5 mA cm-2 and a remarkable applied bias photon-to-current efficiency (ABPE) of 5.3% under simulated AM 1.5 (100 mW cm-2) illumination. The anti-corrosion silicide layer effectively protects Si, ensuring excellent stability of the SR Ni0.95Pt0.05Si/p-Si photoelectrode. This study highlights the potential for achieving efficient PEC HER using bimetallic silicide/Si photocathodes with reduced Pt consumption, offering an auspicious perspective for the cost-effective conversion of solar energy to chemical energy.

Real-Time TEM Observation of the Role of Defects on Nickel Silicide Propagation in Silicon Nanowires

Metal silicides have received significant attention due to their high process compatibility, low resistivity, and structural stability. In nanowire (NW) form, they have been widely prepared using metal diffusion into preformed Si NWs, enabling compositionally controlled high-quality metal silicide nanostructures. However, unlocking the full potential of metal silicide NWs for next-generation nanodevices requires an increased level of mechanistic understanding of this diffusion-driven transformation. Herein, using in situ transmission electron microscopy (TEM), we investigated the defect-controlled silicide formation dynamics in one-dimensional NWs. A solution-based synthetic route was developed to form Si NWs anchored to Ni NW stems as an optimal platform for in situ TEM studies of metal silicide formation. Multiple in situ annealing experiments led to Ni diffusion from the Ni NW stem into the Si NW, forming a nickel silicide. We observed the dynamics of Ni propagation in straight and kinked Si NWs, with some regions of the NWs acting as Ni sinks. In NWs with high defect distribution, we obtained direct evidence of nonuniform Ni diffusion and silicide retardation. The findings of this study provide insights into metal diffusion and silicide formation in complex NW structures, which are crucial from fundamental and application perspectives.

Perspectives and Trends in Advanced MXenes-Based Optical Biosensors for the Recognition of Food Contaminants

Fabricating novel biosensing constructs with high sensitivity and selectivity is highly demanded in food contaminants detection. In this prospect, various nanostructured materials were envisaged to build (bio)sensors with superior sensitivity and selectivity. The desirable biocompatibility, brilliant mechanical strength, ease of surface functionalization, as well as tunable optical and electronic features, portray 2D MXenes as versatile scaffolds for biosensing. In this review, we overviewed the state-of-the-art MXenes-based optical biosensing devices to detect mycotoxins, pesticide residues, antibiotic residues, and food borne-pathogens from foodstuff and environmental matrices. Firstly, the synthesis methods and surface functionalization/modification of MXenes are discussed. Secondly, according to the target analytes, we categorized and presented a detailed account of the newest research progress of MXenes-based optical probes for food contaminants monitoring. The efficiency of all the surveyed probes was assessed on the basis of important factors like response time, detection limit (DL), and sensing range. Lastly, the necessity and requirements for future advances in this emerging MXenes material are also given, followed by challenges and opportunities. We hope that this study will bridge the gap between nanotechnology and food science, offering insights for engineers or scientists in both areas to accelerate the progress of MXenes-based materials for food safety detection.