Enhancing Water Oxidation Activity by Tuning Two-Dimensional Architectures and Compositions on CoMo Hydr(oxy)oxide

To fabricate low-cost and highly efficient two-dimensional (2D) alloyed catalysts, the effect of architectures and compositions on their water oxidation activity should be investigated. Focusing on this, we systematically studied cobalt-molybdenum hydr(oxy)oxide (CM) nanosheets (CM-NSs) and nanoflakes (CM-NFs) with tunable compositions as model catalysts. Comparative spectroscopic analyses of the CM samples with synthesized CoMoOx, MoO3, and alpha-Co(OH)(2) represent that Mo elements in CM-NS are highly dispersed as [MoO4] analogous to CoMoOx, whereas no active vibration modes of [MoO4] are detected in CM-NF. Moreover, CM-NS possesses a relatively higher surface area and abundant oxygen defects. The CM-NS exhibits the lowest overpotential of 377 mV to achieve 10 mA/cm(2) at 12.8 pH and a Tafel slope of 41.88 mV/dec, with robust durability compared to nanoflake (CM-NF) catalysts. In addition, it also outperforms the commercial RuO2 and its annealed rigid structure. The turn over frequency (TOF) calculation further demonstrates rapid kinetics (1.7 times) of nanosheets (CM-NSs) rather than nanoflakes (CM-NFs) at eta = 350 mV. The details of the mechanistic pathway indeed illustrate a defect-induced decoupled proton-electron transfer process for the catalytic framework of 2D nanosheets (CM-NSs). This finding shows a remarkable advantage of porous 2D nanomaterials and highlights a perspective on the contribution of defects for superior electrocatalytic network fabrication.