Quantum Efficiency of Electron Photoinjection from Magnesium into a Nonaqueous Electrolyte

Harnessing light energy through its interaction with metals remains a long-standing challenge. While noble metal plasmonics have been studied extensively, their high cost is a limiting factor. This motivates research into abundant and inexpensive metals with low work functions, such as magnesium. We report electron photoinjection from a magnesium electrode into dimethyl sulfoxide (DMSO). The electrode was biased (−1.0 to −2.5 V vs Ag/AgCl) and illuminated with light (350–600 nm), and the photocurrent was measured. As a function of increasing photon energy, the quantum efficiency of photoinjection initially increases exponentially. However, beyond a threshold energy of 2.95 ± 0.07 eV, it follows a power law with an exponent ∼5/2, consistent with above-threshold electron injection into the conduction band of DMSO. Comparison of the observed threshold to the vacuum work function of magnesium suggests that the conduction band of DMSO is ∼0.71 eV lower than the vacuum level. The quantum efficiency increases at more negative potentials, reaching ∼10–4, a quantity comparable to plasmonic noble metal electrodes. This study will open opportunities to exploit magnesium as an inexpensive and versatile material for metal photoelectrochemistry and potentially magnesium plasmonics.