Greenly Synthesized Conducting Polymer Nanotunnels with Metal-Hydroxide Nanobundles in Single Dais for Unmitigated Water Oxidation.

Abstract

Electrochemical water splitting required efficient electrocatalysts to produce clean hydrogen fuel. Here, we adopted greenway coprecipitation (GC) method to synthesize conducting polymer (CP) nanotunnel network affixed with luminal-abluminal CoNi hydroxides (GC-CoNiCP), namely, GC-Co₁Ni₂CP, GC-Co_1.5Ni_1.5CP, and GC-Co₂Ni₁CP. The active catalyst, GC-Co₂Ni₁CP/GC, has low oxygen evolution reaction (OER) overpotential (307 mV) and a smaller Tafel slope (47 mV dec^-1) than IrO₂ (125 mV dec^-1). The electrochemical active surface area (EASA) normalized linear sweep voltammetry (LSV) curve exhibited outstanding intrinsic activity of GC-Co₂Ni₁CP, which required 285 mV to attain 10 mA cm^-2. At 1.54 V, the estimated turnover frequency (TOF) of GC-Co₂Ni₁CP/GC (0.017337 s^-1) was found to be 3-fold higher than that of IrO₂ (0.0014 s^-1). Furthermore, the GC-Co₂Ni₁CP/NF consumed a very low overpotential (281 mV) with a small Tafel slope of 121 mV dec^-1. The ultrastability of GC-Co₂Ni₁CP for industrial application was confirmed by durability at 10 and 100 mA cm^-2 for the OER (GC/NF-8 h, 2.0%/100 h, 2.2%) and overall water splitting (100 h, 3.8%), which implies that GC-Co₂Ni₁CP had adequate kinetics to address the elevated rates of water oxidation. The effect of pH and addition of tetramethylammonium cation (TMA⁺) reveal that GC-Co₂Ni₁CP follows the lattice oxygen mechanism (LOM). The solar-powered water electrolysis at 1.55 V supports the efficacy of GC-Co₂Ni₁CP in the solar-to-hydrogen conversion. The environmental impact studies and solar-driven water electrolysis proved that GC-CoNiCP has excellent greenness and efficiency, respectively.