Engineering Cobalt Phosphide (CoP) Thin Film Catalysts for Enhanced Hydrogen Evolution Activity on Silicon Photocathodes

Abstract

Transition metal phosphide catalysts have recently emerged as active, earth abundant alternatives to precious metals for the hydrogen evolution reaction in acid. High performance, scalable catalysts are necessary for the successful implementation of photoelectrochemical water splitting devices, which have the potential to generate hydrogen in a sustainable manner. Herein, a general synthetic route is reported to produce transition metal phosphide thin films, which is used to fabricate cobalt phosphide (CoP) catalysts with high average turnover frequency (TOFavg), 0.48 H2 s−1 and 1.0 H2 s−1 at 100 and 120 mV overpotential, respectively. Furthermore, it is shown that CoP thin films can be applied to silicon photoabsorbers to generate one of the most active precious metal‐free crystalline silicon photocathodes to date, achieving −10 mA cm−2 at +0.345 V vs. reversible hydrogen electrode. The synthesis route presented here provides a platform for both fundamental studies of well‐defined electrocatalysts and the fabrication of high‐performance photoelectrodes.

Combining theory and experiment in electrocatalysis: Insights into materials design

“…Ni-Mo systems, exhibit low overpotentials to reach 10 mA cm -2 geo (64)(65)(66). However, such systems also exhibit TOF avg values that are significantly lower than that of Pt, values that are similar to those of non-precious metal systems in acid, hence leaving much room for improvement (64)(65)(66). Homogeneous catalysts with high TOF avg have also been developed, though they typically require large overpotentials to reach appreciable current densities (Fig.…”

“…In addition to catalyst activity, long-term stability is an equally important metric and should be reported in conjunction with activity. Accelerated cyclic voltammetry tests, long-term stability studies that quantify the amount of catalyst leached into the electrolyte, and the use of thin film catalyst morphologies are helpful approaches to assess catalyst durability (10,66).…”

The Predominance of Hydrogen Evolution on Transition Metal Sulfides and Phosphides under CO2 Reduction Conditions: An Experimental and Theoretical Study

“…1 X-ray photoelectron spectroscopy confirmed the formation of the ionic materials based on the presence of a phosphide peak in the P 2p region, a sulfide peak in the S 2p region, and appropriate metal oxidation states which were consistent with previous reports. [1][2] The materials were evaluated for CO2R activity in CO2 sparged 0.10 M KHCO3 using a previously described flow cell. 3 The synthesis for nanoparticulate catalysts is reported elsewhere.…”

Nanostructured p-Type Semiconductor Electrodes and Photoelectrochemistry of Their Reduction Processes

“…Since H 2 is attainable as the reduction product of H + cation it is then mandatory to focus the attention towards p-type electrodes having photoelectrocatalytic properties [62][63][64] towards the reduction of the proton either in the pristine state or with the surface modified by a dye-absorber/photocatalytic agent [65,66]. A comprehensive list of p-type semiconductor cathodes for the photoelectrochemical production of H 2 has been given recently in [67] when the design of optimized photoelectrochemical water splitting cells [68,69] was considered, and solar radiation represented the primary energy source for the activation of this conversion device [70].…”

“…Results of the photoelectrochemical performance achieved with PECs utilizing RGO-based photocathodes are reported in Table 4. Finally, we report now on the photoelectrocatalytic activity of p-Si based photocathodes for HER when silicon has different morphologies (nanowires, micropyramidal, nanomesh), various degree of doping (p-, n + and n + pp + ), and diverse types of photoelectrocatalyst (metallic, p-type semiconducting, metal alloy) [63,97,99,111,[125][126][127][128][129][130][131][132][133][134][135][136][137]. A scheme of the energy levels involved in the interface p-Si/electrolyte for HER is given in Figure 19 [126].…”