Quasi-2D PdSi_2–xGe_xN₄ (x = 0, 1, 2): Promising Candidates for Spontaneous Overall Water Splitting

Abstract

Searching for ecofriendly and highly efficient photocatalysts for renewable energy conversion has been an ongoing challenge. Inspired by the successful synthesis of quasi-2D MoSi 2 N 4 and WSi 2 N 4 , we investigated three members of this family, PdSi 2 N 4 , Janus PdSiGeN 4 , and PdGe 2 N 4 , indicating excellent stability and promising photocatalytic performance using ab initio calculations. All three systems possess appropriate semiconducting band gaps and band edge alignments with robust chemical/dynamical stability. All three systems show excellent hydrogen evolution and oxygen evolution reaction (HER and OER) overpotentials to self-sustain the photocatalytic mechanism. PdGe 2 N 4 turns out to be the best candidate for HER activity, with Gibbs free energy (ΔG) as low as −0.03 eV, even better than that of the traditional Pt catalyst (−0.09 eV). In the case of OER, ΔG is negative for all three systems (under the influence of the potential supplied by photogenerated holes), indicating that the process is spontaneous and no overpotential is required. We strongly believe that the promising photocatalytic performance of these quasi-2D systems reported here will open doors for their future experimental studies.

Theoretical Investigation of Electronic and Photocatalytic Properties of a Trilayer vdW MoS2/ZnO/WS2 Heterojunction for Overall Water-Splitting Applications

“…The potential U is measured with respect to normal hydrogen electrode. The Gibb’s free energy of the adsorbed intermediates in OER steps are presented in eqs – normalΔ G OH * = G OH * + 1 2 G normalH 2 − G normalH 2 normalO − G * − normalΔ G normalU − normalΔ G pH normalΔ G normalO * = G normalO * + G normalH 2 − G normalH 2 normalO − G * − normalΔ G normalU − normalΔ G pH normalΔ G OOH * = G normalOOH * + 3 2 ...…”

“…The potential U is measured with respect to normal hydrogen electrode. The Gibb’s free energy of the adsorbed intermediates in OER steps are presented in eqs – Furthermore, the changes of the free energy in the OER study, For an ideal catalyst, a free energy difference of 1.23 eV is required between continuous intermediate steps to ensure a spontaneous OER activity. However, in real cases, the difference in free energy does not follow as an ideal catalyst, which hinders the OER performance.…”

Palladium-decorated SiX (X = N, P, As, Sb, Bi) catalysts for hydrogen evolution

“…For any material to be used as a photocatalyst, it should possess a suitable electronic band gap (<3 eV) to have maximum photon absorption, high carrier mobility, better charge separation, etc. 9,10 Noble metals like platinum and its alloys show outstanding HER activity, but its high cost and scarcity restricts its application in industry. 6,9,11 Thus, there is a need to develop suitable catalysts with low cost and high efficiency for practical implementation of the HER.…”

Tunable structural phases and electronic properties of group V MSi2N4 (M = V, Nb, Ta) nanosheets via surface hydrogenation: a first-principles study

“…13,14 The VSi 2 N 4 system could even become a valley half-metal through the strain or electric field modulation, 15,16 and the NbSi 2 N 4 nanosheet will exhibit superconductivity with a high transition temperature of 30 K. 17 The T-phase geometry is preferred in the ZrGe 2 N 4 and PdSi 2 N 4 systems, which are both semiconductors with direct and indirect gaps, respectively. 18,19…”

“…systems, which are both semiconductors with direct and indirect gaps, respectively. 18,19 The distinctive structural and electronic properties of these MSi 2 N 4 systems result in their having potential for applications in transistors, photocatalysts, batteries and sensors. 3 It has been proposed that the VSi 2 N 4 nanosheet is a promising anode material for alkali metal ion batteries, which possess high specific capacities and low average open-circuit voltages.…”