Template Electro-Etching-Mediated FeOOH Nanotubes as Highly Efficient Photoactive Electrocatalysts for Oxygen Evolution Reaction

A fast, controlled, and low-cost technique for synthesis of catalysts with (photo)­electro­chemical oxygen evolution reaction (OER) activity is the key to developing (solar) electricity-driven water splitting. Here, we design a template electro-etching strategy to fabricate uniform FeOOH nanotubes (CC@​FeOOH-NTs) as photo­active electro­catalysts, where the in situ conversion process of template etching and electrodeposition completes in less than 400 s. The structural stability of the nanotubes’ morphology and phase transition from β-FeOOH to amorphous after thermal treatments are both determining factors to improve the activity and stability. The optimized CC@​FeOOH-NTs-240 °C presents a low overpotential (η) of 328 mV, to achieve a current density of 10 mA cm–2 with a small Tafel slope of 42 mV dec–1, and maintains its structural integrity and catalytic activity after 15 h. Under visible light irradiation, the photon-excited charge carriers decrease the overpotential to 280 mV (onset) and increase the current density to 16 mA cm–2 (η = 343 mV), 2.7 times higher than the value in the darkness

Effect of Transport Properties of Crystalline Transition Metal (Oxy)hydroxides on Oxygen Evolution Reaction

Electronic transport plays a pivotal role in the electrolysis of semiconducting electrocatalysts for oxygen evolution reaction (OER), while it is mostly underestimated and largely unexplored. Here, by investigating the electronic transport behavior of seven archetypical crystalline Co/Ni/Fe-based (oxy)­hydroxides (unary, binary, and ternary) under OER potential, we study how and the extent to which it affects the apparent catalytic performances. The electronic transports of unary metal (oxy)­hydroxides follow the order of Co > Ni > Fe, and their binary or ternary compounds can generally impose one order of magnitude higher electrical conductivity. By studying the dependence of catalytic performances on electrical conductivities, we further unveil that charge transportability not only determines the electronic accessibility of catalytic nanoparticles but also, to our surprise, regulates the reaction kinetics of the electronically accessible active sites. Remarkably, the regulation extent of reaction kinetics correlates with the electrical conductivities of electrocatalysts, suggesting that the electrocatalytic process is strongly coupled with electronic transport. The work presents an overview of electronic transports of crystalline (oxy)­hydroxides under OER potentials and highlights their pivotal role in unfolding catalytic potential, holding both fundamental and technical implications for the screen and design of efficient electrocatalysts

Oxygen Vacancies Unfold the Catalytic Potential of NiFe-Layered Double Hydroxides by Promoting Their Electronic Transport for Oxygen Evolution Reaction

Oxygen vacancies (Ov) engineering has demonstrated tremendous power to expedite electrocatalytic kinetics for oxygen evolution reaction (OER). The mechanism is elusive, and most of them were attributed to the decoration or creation of active sites. Here, we report the critical role of superficial Ov in enhancing the electronic transport, thereby unfolding the catalytic potential of NiFe-layered double hydroxides for OER. We reveal that the superficial Ov engineering barely regulates the intrinsic catalytic activities but lowers the charge transport resistances by more than one order of magnitude. Loading-dependent electrochemical analysis suggests that the superficial Ov engineering intensively modulates the utilization rate of electronically accessible active sites for OER catalysis. By correlating catalytic activities to charging capacitances of CΦ (related to the absorption of reaction intermediates), we unveil a linear dependence, which indicates switchable catalysis on electronically accessible active sites. Based on the unified experimental and theoretical analysis of the electronic structures, we propose that the superficial Ov imposes electron donation to the conductive band of NiFeOOH, thereby enabling the regulation of electronic transport to switch on/off OER catalysis. The switch effect holds fundamental and technical implications for understanding and designing efficient electrocatalysts