Room-temperature chemical looping hydrogen production mediated by electrochemically induced heterogeneous Cu(I)/Cu(II) redox

Abstract

The chemical looping process is a promising technology for high-purity hydrogen production. However, this process is operated at high temperature (e.g., >600°C), leading to rigorous requirements in the aspects of reactor design and oxygen carriers. Here, we develop a room-temperature electrocatalytic chemical looping hydrogen production system using Cu(OH) 2 as the oxygen carrier and ascorbate as the fuel. The electrolyzer is assembled by coupling cathodic hydrogen evolution and anodic Cu 2 O electro-oxidation. Ascorbate acts as the reducible fuel to reduce the resultant Cu(OH) 2 into Cu 2 O and completes the redox loop. The assembled electrolyzer achieves a current density of 100 mA cm −2 at 0.94 V. The required electricity input per cubic hydrogen produced is 2.57 kWh Nm −3 H 2 , almost half of that for conventional water electrolysis (4.83 kWh Nm −3 H 2 ). This work not only provides a new approach for hydrogen production but also facilitates the development of an innovative catalytic process. • A room-temperature electrocatalytic chemical looping H 2 production system was reported • Operando methods revealed that RTECL works on the basis of Cu(OH) 2 /Cu 2 O redox • The electricity input for hydrogen produced is merely 2.57 kWh Nm 3 H 2 for RTECL As an ideal hydrogen production method, water electrolysis is limited by its high energy consumption because of oxygen evolution reaction with sluggish kinetics. A room-temperature electrocatalytic chemical looping (RETCL) hydrogen production system using Cu(OH) 2 as the oxygen carrier was reported. A two-step indirect process was demonstrated, including an electrocatalytic-driven catalyst oxidation reaction from Cu 2 O to Cu(OH) 2 and spontaneous redox reaction between Cu(OH) 2 and ascorbate to form Cu 2 O and dehydroascorbic acid. The assembled RETCL hydrogen production system needs only 0.94 V to drive 100 mA cm −2 and realizes electricity consumption as low as 2.23 kWh Nm −3 H 2 (half of that of sole water electrolysis). Ultra-low electricity consumption for hydrogen production was achieved based on a room-temperature electrocatalytic chemical looping (RETCL) hydrogen production system. A two-step, Cu(OH) 2 -mediated indirect process was proved for the RETCL system that the pivotal specie Cu(OH) 2 is generated by the electrically driven oxidation of Cu 2 O and spontaneously undergoes redox reaction with ascorbate to reform Cu 2 O, achieving electricity consumption of 2.23 kWh Nm −3 H 2 .