Perspective pubs.acs.org/JPCL
Recent Development in Hydrogen Evolution Reaction Catalysts and Their Practical Implementation Peter C. K. Vesborg,* Brian Seger, and Ib Chorkendorff Center for Individual Nanoparticle Functionality (CINF), Department of Physics, Technical University Denmark, 2800 Kongens Lyngby, Denmark S Supporting Information *
ABSTRACT: The past 10 years have seen great advances in the field of electrochemical hydrogen evolution. In particular, several new nonprecious metal electrocatalysts, for example, the MoS2 or the Ni2P family of materials, have emerged as contenders for electrochemical hydrogen evolution under harsh acidic conditions offering nearly platinum-like catalytic performance. The developments have been particularly fast in the last 5 years, and the present Perspective highlights key developments and discusses them, along with hydrogen evolution in general, in the context of the global energy problem.
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ne of the great advantages of fossil fuels is that they store free energy in concentrated form. Furthermore, it is quite easy to extract this energy via combustion. Fossil fuels are, however, complex molecules that take millions of years to form from natural processes. A much simpler way to store energy is electrolysis of water into a hydrogen fuel and an oxygen byproduct. Thus, to a large extent, the drive to understand and improve electrolysis catalysis is directly related to the possibility of replacing fossil fuels with hydrogen as the world’s primary fuel source. Interestingly, although many Reviews and Perspectives go in-depth into the science behind electrolysis catalysis,1 few relate how this work translates into fulfilling society’s energy needs. Thus, in this Perspective, we will first briefly analyze society’s energy demands with regards to this topic and then analyze the progress of H2 evolution catalysts working in an acidic environment. Global Electricityand the Promise of Hydrogen. Using electrolysis of water to generate hydrogen (and oxygen) to store excess electricity is an old idea.23 [Perhaps first in science fiction: Jules Verne, “Vingt mille lieues sous les mers: Tour du monde sous-marin”, 1870. Poul la Cour pioneered electrochemical storage of wind power as electrolyzed water. He ran illumination of a school in Denmark on hydrogen from windelectrolysis in 1895.] However, only recently has a situation started to emerge in many electricity grids where a substantial fraction of total electricity supply is coming from intermittent renewable resources (notably wind turbines and photovoltaics). Thus, currently, market demand for a practical grid-scale electrolysis technology in order to smooth out intermittent production is still nascent. Nevertheless, there are local markets where electrochemical smoothing would be of great value (see Figure 1). © XXXX American Chemical Society
Figure 1. Danish electricity grid data for October 2014. Denmark has more than 4.8 GW of wind and 0.5 GW photovoltaic power installed. The consumption data (black) shows a nighttime base load of about 2.5 GW and a daytime peak of about 5 GW. Consumption is substantially lower on Saturday and Sunday than on weekdays. In October, there were four nights where wind turbine generation alone (blue) exceeded total consumptionand this despite the fact that, overall, wind power only provided 40% of the overall electricity consumption that month. This illustrates the need for storage.
Zooming out to the global picture, the world produces 2520 GWavg of electricity with an annual growth of 2.5%.4 [IEA estimates the actual “end user” consumption of electricity to be 2170 GWavg. The difference, which is mostly due to conversion and transmission losses, is roughly equivalent to the entire output of the global fleet of commercial nuclear reactors.4] Received: February 11, 2015 Accepted: February 26, 2015
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DOI: 10.1021/acs.jpclett.5b00306 J. Phys. Chem. Lett. 2015, 6, 951−957
The Journal of Physical Chemistry Letters
Perspective
efficiency (above 80%).9 Nevertheless, there are several modes of transportation (e.g., airplanes) where chemical fuels can hardly be substituted for electricity, and these are applications where hydrogen can play a role either directly (e.g., fuel cell (FC) vehicles) or indirectly as a feedstock chemical for hydrocarbon synthesis (Fischer−Tropsch process) or upgrading of, for example, biomass via hydrogenation. A fuel-cell-powered car running on hydrogen has a “grid electricity-to-wheels” overall efficiency of ∼28% (assuming the electrolyzer (EZ) efficiency is 70%10 and the FC-system efficiency is 40%11), which is slightly better than the “tank-towheels” efficiency of a typical ICE car. However, the main economic incentive is to replace the $4.8B/day [as of October 2014] worth of oil that the global transportation system consumes with electricity, and the question is whether a hydrogen based system (i.e., electrolyzer + fuel cell) can compete on a $/W basis. Importantly, the $/W benchmark is more sensitive to capital costs of the electrolyzer (EZ) and FC units than it is to the thermodynamic efficiency. Because the capital cost is a central parameter, it might preclude the use of expensive materials, such as platinum, as electrocatalysts for the hydrogen evolution reaction (HER) in future electrolyzer designs, though the electrocatalyst is only a minor cost item (
