Approaching the Volcano Top: Iridium/Silicon Nanocomposites as Efficient Electrocatalysts for the Hydrogen Evolution Reaction

Abstract

Electrolysis of water to generate hydrogen is an important issue for the industrial production of green and sustainable energy. The best electrocatalyst currently available for the hydrogen evolution reaction (HER) is platinum. We herein show that iridium can be manipulated to achieve a record high HER activity surpassing platinum in every aspect: a lower overpotential at any given current density, a higher current density, and mass activity for all bias potentials applied and a catalyst cost reduction of 50% for the same hydrogen generation rate. The superior HER activity was achieved by a binary Ir/Si nanowire catalyst design in which (as density functional theory calculations show) two distinct strategies act in synergy: (i) decreasing the size of the iridium nanoparticles to ∼2.2 nm and (ii) dividing the H2-generation process to three steps occurring on two different catalysts: H adsorption on iridium, H diffusion to silicon, and H2 desorption from silicon.

Transition Metal Selenides for Electrocatalytic Hydrogen Evolution Reaction

“…Acquiring from the polarize curve, due to the simplicity and convenience, the overpotential at 10 mA cm −2 ( η 10 ) has been widely adopted as the normalized metric to gauge the activity of catalysts . For the sake of industrial production, high current density to the order of 1 A cm −2 are commonly required, so researchers also use other current density value to evaluate the activity of catalysts, as shown in Figure b–c …”

“…Schematic representation of the "Volmer-H diffusion-Tafel" or the Volmer-H diffusion-Heyrovsky" reaction pathway. Reproduced with permission from Ref [19]…”

Hydrogen Evolution Reaction on Iridium-Modified Nickel Foam Surfaces

“…Also, the reported j 0 values [20] were 2.9 × 10 −4 and 4.6 × 10 −4 A cm −2 for Ir and Ir-Ni electrodes, correspondingly. On the other hand, Sheng et al [28] reported an exchange current-density value of 8.18 × 10 −6 A cm −2 on iridium-modified (17.7 wt.%) silicon nanowire structure in 0.5 M H 2 SO 4 solution. Finally, Vazquez-Gomez et al [8] examined the HER behavior of iridium-modified porous Ni layers in 0.1 M NaOH and recorded very high values of the j 0 , on the order of 7.2 × 10 −3 to 1.2 × 10 −2 A cm −2 .…”

A fundamental viewpoint on the hydrogen spillover phenomenon of electrocatalytic hydrogen evolution

“…Especially, by normalizing to the noble-metal weight loading, the Pt 2 Ir 1 /CoP catalysts gave a mass activity as high as 110 A•mg PtIr −1 at overpotential of -50 mV vs RHE, which was 78 times higher than that of the commercial HER catalyst (20 wt% Pt/C, 1.4 A•mg Pt −1 ) and even an order of magnitude higher than that for the state-of-the-art noblemetal HER electrocatalysts under the similar operation conditions (Figure 4c). 21,23,26,[38][39][40][41][42][43][44][45][46][47][48][49][50][51] This value represents the highest noble-metal utilization activity for HER so far, demonstrating the importance of our primary understandings on the hydrogen spillover of binary metal/support catalysts.…”

“…Inspired by the hydrogen spillover phenomenon in thermal hydrogenation through the strong metalsupport interaction, 19,20 recently, hydrogen spillover has emerged as a new frontier in the binary metal/support HER electrocatalysts, [21][22][23][24][25][26] which undergoes (1) the strong proton adsorption on metals (∆G H-metal < 0); (2) the interfacial hydrogen spillover from metals to supports and (3) e cient hydrogen desorption on supports (∆G H-support > 0). This strategy affords a new concept by integrating both advantages of metal and support and thereby kinetically promotes the proton adsorption and hydrogen desorption.…”