Nanoscale palladium as a new benchmark electrocatalyst for water oxidation at low overpotential

Abstract

There is an overwhelming desire to discover new catalytic materials for efficient water oxidation that perform at low overpotentials (below 1.50 V vs. RHE), and which exhibit tremendous stability along with high oxygen evolution reaction (OER) current density over a small potential window. However, it remains a challenge to establish a competent solar to fuel conversion system. We present here the first example of a nanoscale nanoporous Pd-derived benchmark material used as a highly stable and low overpotential electrocatalyst for water oxidation. The Pd electrocatalyst executes water oxidation at an onset potential of just 1.43 V vs. RHE; η = 200 mV. The catalyst also exhibits remarkable performance for OER, reaching a current density of 10 mA cm⁻² at 1.47 V (η = 240 mV), and with a current density of 100 mA cm⁻² achieved at only 1.63 V (η = 400 mV), which represents better OER activity than that of the benchmark IrO₂ electrocatalyst (301 mV and 313 mV required to drive a current density of 10 mA cm⁻²). Furthermore, the catalyst demonstrates a Tafel slope of 40 mV dec⁻¹, a high mass activity of 560 mA mg⁻¹ (MA) and a large TOF value of 0.2 s⁻¹, and exhibits remarkable long-term stability for use in oxygen evolution experiments. A thin-film Pd electrocatalyst was obtained via the Aerosol-Assisted Chemical Vapor Deposition (AACVD) method on conducting surfaces. XRD and XPS analyses showed a phase-pure crystalline metallic Pd deposit. A surface morphology study revealed a nanoparticulate highly porous nanostructure. Our study reveals a straightforward method for the development of the first example of a Pd-derived nanoporous electrocatalyst for high-efficiency water oxidation and for chemical energy conversion.