Recent Methods for the Synthesis of Noble-Metal-Free Hydrogen-Evolution Electrocatalysts: From Nanoscale to Sub-nanoscale

Abstract

renewable energy resources should be integrated with some energy storage and conversion devices. [10,11] In particular, the electrochemical splitting of water to generate hydrogen (H 2 ) and oxygen (O 2 ) seems to provide an appealing solution through conversion of the electrical input driven by the intermittent energies into stable chemical fuel. [12][13][14][15] As H 2 contains the highest specific energy (141.86 MJ kg −1 ) than all chemicals, it is considered to be a promising energy carrier. The strategy of electrochemical water splitting is conceptually simple, as illustrated by Figure 1. In a typical water-electrolysis cell, the cathode and anode are incorporated into compartmentalized spaces separated by an ion-exchange membrane. As the electron flow passes through the circuit, protons (or water molecules) are reduced into H 2 at the cathode, termed as the hydrogen-evolution reaction (HER); in the meantime, water molecules (or hydroxide ions) are oxidized into O 2 at the anode, termed as the oxygen-evolution reaction (OER). The thermodynamic voltage to commence water splitting is commonly greater than 1.23 V, whereas to achieve high reaction rates, an additional driving force in the form of an overpotential (η) (around 0.7 to 1.0 V) [16] is needed to overcome the kinetic barriers of both the HER and the OER, which determines the conversion efficiency, from electrical to chemical energy.To minimize the η while maintaining the high efficiencies of energy conversion, the electrodes in a water electrolyzer are modified with active and stable electrocatalysts to increase the rates of the electrochemical reactions. The cathodic HER involves two-electron transfer and one central intermediate, known as the atomic H chemisorbed on the electrocatalyst surfaces (H*). Its elemental steps are depicted through either the Volmer-Heyrovsky or the Volmer-Tafel mechanism, as seen in Reaction equation (1) to (5): i) Volmer step:

Carbon‐Rich Nonprecious Metal Single Atom Electrocatalysts for CO2 Reduction and Hydrogen Evolution

“…Compared with the deeply investigated OER, [80][81][82] the HER is an inseparable, often overlooked component of water splitting, which has been widely considered to be a sustainable alternative to traditional fossil fuels. [83][84][85][86][87][88][89] The two-electron pathway of HER process is usually divided into two theoretical mechanisms in acid solution [90]…”

Prereduction of Metal Oxides via Carbon Plasma Treatment for Efficient and Stable Electrocatalytic Hydrogen Evolution

“…Hydrogen evolution from water splitting offers a sustainable method to acquire molecular hydrogen (H 2 ) fuel, an ideal alternative to fossil fuels without CO 2 emission . To make this technology viable, the catalyst in an electrolysis device should exhibit both high electrocatalytic activity and long‐term durability.…”

“…Hydrogen evolution from water splitting offers a sustainable method to acquire molecular hydrogen (H 2 ) fuel, an ideal alternative to fossil fuels without CO 2 emission. [1][2][3][4] To make this technology viable, the catalyst in an electrolysis device should exhibit both high electrocatalytic activity and long-term durability. In this regard, catalysts based on precious metals, such as Pt, meet the above-mentioned characteristics, but their scarcity, high cost and poor stability are hindrance to any large-scale prereduction of metal oxides.…”

“…[34] To further check their chemical stability, the NiMoO 4 , H 2 -1h, and C-30s samples were immersed in 1 m KOH solution for 12 h (without electrochemical measurement). We found the nanowire arrays of the NiMoO 4 not the C-30s ( Figure S8, Supporting Information). This indicates that the carbon shell effectively protects the active materials from dissolution in KOH solution.…”

CoP‐Doped MOF‐Based Electrocatalyst for pH‐Universal Hydrogen Evolution Reaction

“…[1] One of the most promising methods to produce high-purity hydrogen is electrocatalytic water splitting, which primarily involves hydrogen evolution reaction (HER). [3] Recently,transition metal phosphides (TMPs) have been regarded as ac lass of advantageous HER catalysts due to their hydrogenase-like catalytic mechanism. [3] Recently,transition metal phosphides (TMPs) have been regarded as ac lass of advantageous HER catalysts due to their hydrogenase-like catalytic mechanism.…”