CO 2 electroreduction activity and dynamic structural evolution of in situ reduced nickel-indium mixed oxides

In the field of CO 2 electroreduction (CO 2 ER), tuning the selectivity among diverse products remains a major challenge. Mixed metal catalysts offer possible synergetic effects which can be exploited for tuning product selectivity. We present a simple wet chemical approach to synthesize a range of nickel-indium mixed oxide (Ni A In B Ox) thin films with homogeneous metal distribution. CO 2 electroreduction results indicate that the Ni A In B Ox mixed oxide thin films can achieve high CO selectivity (>70%) in contrast with the single metal oxides NiO (H 2 >90%) and In 2 O 3 (formate >80%). The relative composition Ni 40 In 60 Ox attained the best CO selectivity of 71% at moderate cathodic bias of −0.8 V RHE , while a higher cathodic bias ( E < −0.9 V) promoted a decrease of CO in favor of formate. A detailed investigation of the Ni 40 In 60 Ox thin films following progressive stages of reduction during CO 2 ER revealed dynamic structural transformations strongly dependent on applied bias and electrolysis time. For the CO-selective catalyst composition, at moderate cathodic bias ( E < −0.8 V) and short electrolysis times (1 h), the catalyst is composed of nickel-indium alloy grains embedded in amorphous Ni–In mixed oxide as observed by electron microscopy. Extending electrolysis time at −0.8 V for 10 h, or increasing the applied reductive bias to −1.0 V, result in a complete reduction of the residual oxide film into an interconnected array of multicomponent (In, Ni, Ni 3 In 7 ) nanoparticles which display significantly lower CO selectivity (