Under the goals of carbon neutrality and sustainable energy development, green hydrogen production and biomass resource utilization have become important topics in energy-related education and research. The hydrogen evolution reaction (HER) is a key process in electrocatalytic water splitting, and the development of highly efficient, low-cost catalysts is essential for improving hydrogen production efficiency. Although Pt–based catalysts show outstanding HER activity, their high cost and limited availability hinder their large-scale application. Loading Pt as isolated atoms onto biomass–derived carbon can increase the utilization efficiency of noble metals while taking advantage of the pore structure and surface functional groups of biochar. Based on the concept of integrating scientific research with undergraduate teaching, this study develops a comprehensive laboratory experiment using walnut shell–derived biochar–supported Pt single-atom catalysts for the HER. The experiment is designed to help students understand the correlations among biomass conversion, catalyst structure regulation, and electrochemical performance evaluation, thereby improving their understanding of frontier electrocatalysis and green energy technologies.

Walnut shell was selected as the biomass precursor. After crushing and sieving, the powder was converted into biochar through high-temperature pyrolysis, followed by KOH activation with different mass ratios to obtain carbon supports with different pore structures. Pt species were then introduced onto the biochar surface via an impregnation–adsorption method using chloroplatinic acid as the precursor. The prepared catalysts were designated Pt/HKC, Pt/HKC-0.5, Pt/HKC-1, and Pt/HKC-1.5 according to the activation conditions. The pore structure, morphology, Pt dispersion, and surface chemical states of the samples were analyzed using nitrogen adsorption–desorption, scanning electron microscopy (SEM), aberration-corrected transmission electron microscopy (AC-TEM), and X-ray photoelectron spectroscopy (XPS). Their HER performances were tested in 0.5 mol/L H₂SO₄ using a three-electrode system. Linear sweep voltammetry (LSV), Tafel analysis, and electrochemical impedance spectroscopy were employed to evaluate catalytic activity, reaction kinetics, and charge-transfer behavior, respectively.

The results show that KOH activation plays an important role in regulating the structure of walnut shell–derived biochar. Compared with the non-activated sample, the activated biochars possess more developed pore structures and larger surface areas. Among them, HKC-0.5 exhibits the most suitable textural properties, with a specific surface area of 839.32 m²/g and a pore volume of 0.49 cm³/g. This porous structure provides abundant anchoring sites for Pt and facilitates electrolyte transport. SEM observations reveal that moderate activation creates abundant pores, while excessive activation partially damages the carbon framework. AC-TEM images verify that Pt is predominantly dispersed as isolated atoms on the biochar support. XPS analysis further suggests strong interactions between Pt species and oxygen-containing functional groups, which help stabilize the single-atom structure. Electrochemical measurements demonstrate that Pt/HKC-0.5 exhibits the best HER performance, requiring an overpotential of only 25 mV at a current density of 10 mA/cm², with a Tafel slope of 58 mV/dec and a charge-transfer resistance of 2.1 Ω. These results indicate that appropriate pore regulation enhances Pt dispersion, promotes interfacial electron transfer, and increases Pt utilization efficiency.

This experiment combines biomass-derived carbon preparation, single-atom catalyst synthesis, structural characterization, electrochemical testing, and data analysis into a coherent teaching module. By comparing samples prepared under different activation conditions, students can better understand how the pore structure of biochar affects Pt dispersion and HER activity. The experiment also encourages students to move beyond routine experimental procedures and develop the ability to analyze structure–performance correlations based on experimental data. It is suitable for senior undergraduates majoring in energy, chemistry, environmental science, materials science, and related disciplines, and supports the development of comprehensive experimental skills, data analysis capabilities, scientific communication skills, and innovation awareness.