Novel superhydrophilic/superaerophobic NiFe-LDH@Ni 100− x Cu x electrodes for efficient OER catalysis

Water splitting is a promising technique to produce green hydrogen, but it is severely limited by sluggish kinetics of the oxygen evolution reaction (OER). Addressing this issue demands not only efficient OER catalysts but also better electrode structure which can guarantee effective and stable utilization of the catalysts. Superhydrophilic/superaerophobic porous structure is an ideal candidate for gas evolution reactions. However, fabricating such electrodes usually involves complex procedures and harsh conditions. Moreover, the effects of porous structure on electrode hydrophilicity, aerophobicity, and thereby the OER kinetics have not yet been systematically investigated. Herein, using NiFe-LDH as a presentative OER catalyst, we developed a facile two-step electrodeposition method to prepare superhydrophilic/superaerophobic NiFe-LDH@Ni_100-xCu_x electrodes at room temperature. The porous electrode structure was tuned by varying Cu content in the Ni_100-xCu_x scaffolds. It was found that higher hydrophilicity was not always equivalent to better underwater aerophobicity for the porous electrodes since pores with different sizes played different roles. Big pores benefited faster water spreading rate while small pores with lower ligament/pore size ratio enabled larger underwater O₂ bubble contact angles. The NiFe-LDH@Ni₉₅Cu₅ electrode with a hierarchical porous structure displayed both superhydrophilicity and superaerophobicity. Consequently, a small OER overpotential of 286 mV at 300 mA‧cm^-2 was achieved on the NiFe-LDH@Ni₉₅Cu₅, which was 74 mV lower than that on the NiFe-LDH@NF (commercial Ni foam). The outstanding OER catalytic performance of the NiFe-LDH@Ni₉₅Cu₅ electrode and its convenient fabrication technique provide a new strategy for future design and preparation of novel electrodes for efficient gas evolution reactions.