Reducing toxic Cr(VI) to Cr(III) by formic acid attracts much interest for chromium remediation but still needs efficient catalysts to boost its sluggish kinetics. Herein, PdCu nanoalloy (similar to 3 nm) was uniformly immobilized in N-doped carbon/graphene (NCG) porous nanosheets that were derived from the sandwich-like ZIF-8/graphene oxide precursor. The resulting PdCu/NCG showed a high specific area (S-BET) of 656.1 m(2) g(-1) and a superior activity (k(n)) of 38.2 min(-1) mg(-1) for the Cr(VI) reduction with formic acid as reductant, which outperformed its monometallic counterparts and most of noble-metal catalysts. The catalytic performance highly depended on the composition of PdCu nanoalloy and NCG support. DFT calculation and XPS analysis proved the presence of electron transfer from Cu to Pd upon alloying, which induced an upshift of d-band center (epsilon(d)) of PdCu metals with respect to Fermi energy. The elevated ed facilitated the chemisorption and C-H breakage of formic acid to produce active H species on the catalyst. Such alloying-induced electronic modification of PdCu alloy and porous feature of NCG nanosheets both accounted for the catalytic enhancement.