To address CO₂ emissions caused by excessive fossil fuel consumption, a novel Ni-N co-doped biomass-derived carbon catalyst (Ni-NBC-800) is developed using agricultural waste corn stalks, aiming to achieve electrochemical CO₂ reduction (CO₂ Reduction Reaction, CO₂RR) for synthesizing syngas (CO/H₂) with tunable ratios and promote CO₂ resource utilization. A NH₄Cl-assisted pore-forming strategy combined with nickel impregnation and high-temperature pyrolysis is employed to construct a composite catalyst featuring hierarchical porous structures and metal-nitrogen active sites. Experimental results demonstrate that with the optimized mass fraction of the load Ni (2%) and calcination temperature (800 ℃), the catalyst achieved a CO Faradaic efficiency of 72.8% at $-0.8$ V, while the molar ratio of CO to H₂ can be continuously adjusted within the range of 0.75 to 3.15 through potential regulation, meeting downstream syngas process requirements. Compared with commercial activated carbon-based catalyst (Ni-NAC-800), Ni-NBC-800 exhibited superior CO partial current density ( $-4.75$ mA/cm²) and stability (the 24 h current retention rate of 90.3%). Characterization analyses revealed that the hierarchical porous structure formed by NH₃/HCl gas synergistic etching during NH₄Cl pyrolysis significantly enhanced reactant mass transfer and catalytic activity. This work not only validates the feasibility of agricultural waste-derived carbon materials as alternatives to commercial carbon supports, but also provides a new strategy for low-cost and tunable syngas electrosynthesis through metal-support synergistic design.