Incorporation of (Co-Ni)P Based Electrocatalysts in Tin Sulfide Photoelectrodes

Abstract

Ever since the industrial revolution, available energy sources have been closely related to technological development. Therefore, energy has become the main component towards the productivity of industrialized nations. The indiscriminate use of fossil fuel has produced a gradual decrease of oil reserves that affects the worldwide price of this product. The above-mentioned causes uncertainty because price fluctuations in the international value of oil directly affects nation economies.The development of industrialized societies has, unfortunately, proved to be non-sustainable, due to its strong dependency of fossil fuels and the environmental damage produced by the combustion that this kind of fuel generates. Consequently, this has led to a search of alternative energy sources, highlighting technologies based on molecular hydrogen (carrier energy), and photovoltaic devices. However, nowadays the high cost of production of molecular hydrogen makes it necessary to search new alternatives in order to produce it. Thus, photoelectrochemical water splitting becomes an attractive option that should be considered, due to the use of solar energy as a renewable energy source [1]. However, in photoelectrochemical systems, photocurrent loss is one of the biggest problems present. This is a consequence of the recombination process, either of electron-hole pairs or majority carriers with intermediaries bounded to the electrode surface. The latter is caused by slow transfer kinetics between the carriers photogenerated and the reaction intermediaries. On the other hand, the use of electrocatalyst (materials that catalyzes an electrochemical reaction) allows reduce the electric energy consumption of the electrochemical reactions involved in this process. In this way, for electrocatalytic water splitting, studies are centered on electrocatalysts for OER (anodic reaction) and electrocatalysts for HER (cathodic reaction). Thus, electrocatalysts can be a key issue in the study of light-driven overall water splitting systems [2].In this study, the synthesis of different electrocatalysts based on CoP and NiP was carried out through a hydrothermal procedure following by a thermal phosphorization reaction. The electrocatalysts obtained were characterized through X-ray diffraction, scanning electron microscopy, and polarization curves. These characterization techniques confirm the formation of different CoxNi(1-x)P compounds (where 1 ≥ x ≥ 0) showing in some cases an improvement in the kinetic parameters of the hydrogen evolution reaction (HER). In this way, the best performance (Co-Ni)P electrocatalysts were deposited on a SnS surface (p-type semiconductor), which was electrodeposited from an acidic solution employing SnSO4 and Na2S2O3 as tin and sulfur precursors, respectively. The deposition of the electrocatalysts was carried out through spin-coating technique, employing an ethanolic suspension of the (Co-Ni)P compounds. The SnS surface modification with the (Co-Ni)P based electrocatalysts was confirmed through SEM images. Thus, the modified SnS was employed as a photocathode in a photoelectrochemical cell in order to study its performance as an efficient photoelectrode in the hydrogen evolution reaction. In comparison with the unmodified SnS photoelectrode, an improvement in the photoelectrode stability was observed, which is attributed to the presence of electrocatalysts in the SnS surface.Acknowledgement This study was supported by Fondecyt (Chile) project 1210548References A. Grimes, O.K. Varghese, S. Ranjan, Light, water, hydrogen. The solar generation of hydrogen by water photoelectrolysis, Springer, New York, 2008.M. Peter, K.G. Upul Wijayantha, Photoelectrochemical water splitting at semiconductor electrodes: Fundamental problems and new perspectives, ChemPhysChem. 15 (2014) 1983–1995. Figure 1