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Preferential oxidation of CO in H2 (PROX) reaction is a promising solution to the on‐board purification of CO‐contaminated H2 fuel for use in next‐generation proton‐exchange membrane fuel cells (PEMFC). However, achieving high CO selectivity, activity and structural stability across the wide temperature window remains a great challenge. Herein, we fabricate centimeter scale interfacial PROX catalysts grown from nanoporous single‐crystalline Pr2O3 and Nd2O3 monoliths with lattice surface‐deposited Pt clusters at nanoscale. We demonstrate complete and selective removal of CO in H2 over an unprecedented wide temperature window (253–403 K). The monoliths are integrated with an operational PEMFC to purify the H2 fuel contaminated with CO (30 ppm) and enable stable power output for >400 h; over two thousand times longer than without. This work demonstrates that the nanoporous single‐crystalline oxide monoliths can simultaneously achieve the stability and overall performance required to realize practically useful PEMFCs. [ABSTRACT FROM AUTHOR]

This work reports that a low‐temperature thermal calcination strategy was adopted to modulate the electronic structure and attain an abundance of surface‐active sites while maintaining the crystal morphology. All the experiments demonstrate that the new photocatalyst nano MIL‐125(Ti)‐250 obtained by thermal calcination strategy has abundant Ti3+ induced by oxygen vacancies and high specific surface area. This facilitates the adsorption and activation of N2 molecules on the active sites in the photocatalytic nitrogen fixation. The photocatalytic NH3 yield over MIL‐125(Ti)‐250 is enhanced to 156.9 μmol g−1 h−1, over twice higher than that of the parent MIL‐125(Ti) (76.2 μmol g−1 h−1). Combined with density function theory (DFT), it shows that the N2 adsorption pattern on the active sites tends to be from "end‐on" to "side‐on" mode, which is thermodynamically favourable. Moreover, the electrochemical tests demonstrate that the high atomic ratio of Ti3+/Ti4+ can enhance carrier separation, which also promotes the efficiency of photocatalytic N2 fixation. This work may offer new insights into the design of innovative photocatalysts for various chemical reduction reactions. [ABSTRACT FROM AUTHOR]