Developing low-cost, high-performance metal-free electrocatalysts is crucial for sustainable oxygen evolution reactions (OERs) in alkaline media. Here, we synthesized ultra-long boron phosphide (BP) microwires along the [111] crystal axis with high yield. By controlling temperature and adding Ni, we identified Ni's role as a flux and transport agent, optimizing BP microwires at 1050°C. Electrical property and band structure analysis revealed BP as a one-dimensional p-type semiconductor with a wide band gap. We constructed an on-chip electrocatalytic microdevice using individual BP microwires to evaluate OER performance. In 1M NaOH, the BP electrode achieved 50 mA cm