Ni0-rich Ni/NiO nanocrystals for efficient water-to-hydrogen conversion via urea electro-oxidation

It is highly desired to develop low-cost and effective non-precious metal based electrocatalysts for water-to-hydrogen conversion assisted by urea electro-oxidation reaction. In this work, Ni-0-rich Ni/NiO nanocrystals were facilely synthesized on the surface of acid-treated nickel foam via thermal annealing in Ar/H-2 (denoted as NF@Acid-H-2). The three-dimensional free-standing NF@Acid-H-2 electrode exhibited high HER and UOR activities at 156 mV and at 1.33 V to reach the current density of 10 mA/cm(2), respectively. The urea electrolyzer needed a cell voltage of 1.49 V to deliver the current density of 10 mA/cm(2), and could continuously generate H-2 for 20 h with negligible activity loss. Systematic study revealed that the presence of Ni-0 played a significant role to improve both HER and UOR performance. In particular, the Ni-0-rich Ni/NiO exhibited better catalytic performance than that of Ni-0-less counterpart. This work proved that the high urea electrolysis performance was dependent on the rational design of non-precious metal electrocatalysts with controllable compositions and hierarchical nanostructures.