Photoelectrochemical (PEC) nitrogen reduction reaction (NRR), which produces ammonia under ambient conditions by combining the merits of electrocatalysis and photocatalysis, represents an attractive prospect for nitrogen fixation. Limited by the choice of suitable p-type semiconductor, PEC nitrogen fixation should be preferentially achieved by cathodic NRR integrated with photoanode rather than direct photocathodic NRR. Even in such an approach, it still remains elusive how to design catalytically active sites on the dark cathode toward high activity and selectivity in PEC NRR. Herein, we report a new strategy for tailoring cathodic bismuth (Bi) sites with boron (B) doping and rolling curvature. The B doping in Bi matrix greatly reduces the energy barrier of the potential-determining step of N2 → *NNH in NRR while the high curvature surface on nanorolls facilitates the adsorption of N2. The integration of B doping and rolling curvature in a single cathodic catalyst boosts PEC NRR performance when combined with TiO2 nanorods array as photoanode to harvest light and provide photo-generated electrons. Such a PEC system offers an ammonia yield rate of 29.2 mgNH3 gcat.−1 h−1 and Faradaic efficiency of 8.3 % at a bias of 0.48 V versus RHE in nitrogen fixation. This work provides a guideline for the rational design of highly active and selective metallic catalyst in PEC NRR.