Rising Again: Opportunities and Challenges for Platinum-Free Electrocatalysts

It is well-known that platinum (Pt) is the best electrocatalyst currently available. However, its high cost and scarcity have hindered the commercialization of many green technologies that require the use of Pt electrocatalysts. To pave the way for mass production, the search for alternative electrocatalysts was initiated by researchers working in the fuel cell area, and it has been rapidly expanded to other energy applications in the past few years. Our discussion in this perspective starts with several reasons why Pt is the best electrocatalyst for many important electrochemical reactions such as the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER). Along with a brief introduction of other novel metal electrocatalysts (ruthenium and iridium compounds) used for the oxygen evolution reaction (OER), this perspective highlights recent advances in the development of non-Pt electrocatalysts for dye-/quantum-dot-sensitized solar cells (DSSCs/QDSSCs) and water-splitting systems. We identify the key materials in each area that have shown promising results for replacing Pt as an electrocatalyst and discuss their pros and cons. The possible mechanisms responsible for the observed improvements in performance are also discussed. While many materials have shown encouraging electrocatalytic activity, the long-term stability under a variety of operating conditions remains as a critical issue that must be addressed. An improved theoretical understanding is also required to accelerate the progress in this area. The main challenge is to identify the active sites and operating mechanisms in order to intelligently design and synthesize better and more cost-effective electrocatalysts.